Every investor pitch starts with the same question: how big is your market? Whether you are raising a seed round or Series A, your TAM, SAM, and SOM numbers must be both ambitious and defensible. This comprehensive guide teaches you exactly how to calculate, validate, and present market sizing that gets funded.
VCs passed on Airbnb because the market seemed too small. Investors rejected YouTube because video hosting costs seemed unsustainable. Getting market sizing right is not just about big numbers - it is about demonstrating you understand your addressable opportunity, can articulate realistic capture, and know how your market will evolve. This guide shows you how.
When you walk into an investor meeting, your market size slide will receive more scrutiny than almost any other. This is because VCs invest in markets first, teams second, and products third. A brilliant team building an exceptional product in a $50 million market will never generate venture-scale returns. Conversely, a decent team in a massive, rapidly growing market might 10x despite execution mistakes.
Understanding TAM (Total Addressable Market), SAM (Serviceable Addressable Market), and SOM (Serviceable Obtainable Market) is not merely about putting impressive numbers on a slide. It is about demonstrating strategic thinking: Do you understand who your customers are? Can you reach them efficiently? What market share is realistic given competition and resources? How will this market evolve?
This comprehensive guide provides the frameworks, methodologies, and real examples you need to calculate defensible market sizes, avoid the mistakes that get founders laughed out of pitch meetings, and present market opportunity in a way that builds investor confidence rather than skepticism.
TAM, SAM, and SOM are nested market sizing metrics that help investors understand the full market opportunity (TAM), your addressable segment (SAM), and your realistic near-term capture (SOM). Together, they tell the story of market scale, focus, and achievable growth.
TAM represents the total revenue opportunity available if you achieved 100% market share globally with no constraints whatsoever. This is the theoretical maximum - every potential customer, everywhere, buying your product at full price.
Global knowledge workers: 1.25 billion people
Percentage managing projects: 30% = 375 million potential users
Average revenue per user (ARPU): $120/year
TAM Calculation: 375M users x $120 = $45 billion
This assumes you could sell to every project manager on Earth - unrealistic, but establishes the theoretical ceiling.
TAM shows investors the category is large enough to support venture-scale outcomes. Even if you capture just 1-2% of a $50B TAM, that is still a $500M-$1B revenue opportunity. VCs need this headroom to justify investment risk.
SAM is the portion of TAM that you can realistically target given your business model, product capabilities, geographic reach, and go-to-market strategy. SAM accounts for practical constraints like language barriers, regulatory restrictions, and customer segment fit.
TAM: $45 billion (global, all segments)
Geographic focus: North America only = 23% of global TAM
Customer segment: SMB companies (10-500 employees) = 55% of market
Product fit: Tech/creative industries = 40% of SMB segment
SAM Calculation: $45B x 23% x 55% x 40% = $2.3 billion
This represents the realistic addressable market given your current product, team, and GTM capabilities.
SAM shows investors you understand who your actual customers are and that you have a focused strategy. A smaller, well-defined SAM is more credible than claiming you can sell to everyone. SAM also helps VCs evaluate your go-to-market efficiency.
SOM is the realistic portion of SAM you can capture in the near term - typically over the next 3-5 years - given competition, your sales and marketing capacity, customer acquisition costs, and execution capabilities. SOM is where your financial projections meet your market sizing.
SAM: $2.3 billion (North America SMB tech/creative)
Market share goal (Year 5): 3% (realistic given 20+ competitors)
SOM Calculation: $2.3B x 3% = $69 million
Customer acquisition math:
- Total addressable customers: 1.9M companies x $120 ARPU = $2.3B SAM
- Target customers by Year 5: 575,000 companies
- Realistic conversion with sales team: 3% = 17,250 customers
- Revenue: 17,250 x $4,000 ACV = $69M
This SOM ties to your actual 5-year revenue projections and sales capacity modeling.
SOM is the number VCs will actually validate against your financial model. If you project $100M in Year 5 revenue but your SOM is only $50M, investors will immediately question your assumptions. Your SOM must support your revenue trajectory with realistic conversion and sales capacity assumptions.
Each metric narrows the focus from theoretical maximum (TAM) to your strategic target (SAM) to realistic near-term capture (SOM).
Top-down market sizing starts with total industry data from analyst firms like Gartner, IDC, Forrester, or Statista, then applies filters to narrow to your addressable segment. This approach is fast and leverages credible third-party research, but can miss customer-level nuances.
Start with total market size from industry analyst reports. Look for recent data (within 12-18 months) from credible sources. VCs recognize and trust specific research firms.
Technology Markets
General Business
Gartner reports the global CRM software market at $69.5 billion in 2025, growing at 12% CAGR. This becomes your TAM starting point. Always cite the source, year, and CAGR in your pitch deck.
Unless you are truly global from day one, narrow to your target geographies. Use standard regional breakdowns with percentage of global market.
| Region | Typical % of Global Tech Market |
|---|---|
| North America (US + Canada) | 40-45% |
| United States only | 38-42% |
| Europe (EU + UK) | 25-30% |
| Asia-Pacific | 20-25% |
| Rest of World | 5-10% |
Note: Consumer markets vary significantly - US is often 25-30% of global consumer spending.
Narrow to your ideal customer profile (ICP) by company size, industry, or customer type. Enterprise, mid-market, and SMB have different market sizes and buying behaviors.
| Segment | Employees | % of Total Market | ACV Range |
|---|---|---|---|
| Enterprise | 1,000+ | 25-35% | $50K-$1M+ |
| Mid-Market | 100-1,000 | 30-40% | $10K-$50K |
| SMB | 10-100 | 25-35% | $1K-$10K |
| Micro/Solopreneur | 1-10 | 5-15% | $100-$1K |
Finally, narrow to the specific product category or use case your solution addresses. A broad category like CRM might need filtering to sales automation, customer success, or marketing automation.
Starting TAM: $69.5B global CRM market (Gartner 2025)
Geographic filter: x 42% (US market) = $29.2B
Segment filter: x 35% (SMB companies) = $10.2B
Category filter: x 25% (sales automation specifically) = $2.6B
Final SAM: $2.6 billion (US SMB sales automation)
Source: Gartner CRM Market Guide 2025, US Census Bureau business statistics, internal market analysis
Bottom-up market sizing builds from actual customer counts and unit economics. This approach is more defensible than top-down because it demonstrates you have counted real customers, understand pricing, and can validate your assumptions with data. VCs prefer bottom-up for SAM and SOM calculations.
Identify and count every potential customer that fits your ICP. Use census data, industry databases, LinkedIn Sales Navigator, ZoomInfo, or your own market research to get precise customer counts.
B2B Customer Counts
B2C Customer Counts
ICP: US tech companies with 50-500 employees that are Series A+ funded
Data sources:
- Crunchbase: 14,300 US Series A+ tech companies
- Filter by employee count (50-500): 8,600 companies
- Validate with LinkedIn Sales Navigator: 8,200 companies
Total addressable customers: 8,200 companies
Determine how much revenue you will generate per customer annually. For SaaS, this is your Annual Contract Value (ACV). For usage-based or transaction models, calculate average annual spend based on customer behavior data.
SaaS Subscription
Monthly price x 12 months x (1 - churn rate) = Annual Contract Value (ACV)
Example: $99/month x 12 x (1 - 0.05) = $1,128 ACV
Per-Seat Pricing
Average seats per customer x price per seat x 12 months
Example: 15 seats x $29/seat/month x 12 = $5,220 ACV
Marketplace/Transaction
Average GMV per customer x take rate x 12 months
Example: $50,000 GMV x 8% take rate = $4,000 revenue per customer
Usage-Based
Average monthly usage x price per unit x 12 months
Example: 100,000 API calls/month x $0.01/call x 12 = $12,000 ACV
Multiply your total addressable customer count by your average revenue per customer. This gives you a bottom-up TAM that you can cross-validate against your top-down calculation.
Total addressable customers: 8,200 US Series A+ tech companies (50-500 employees)
Average revenue per customer: $15,000 ACV
- Pricing: $49/employee/month
- Average customer size: 150 employees
- Adoption rate: 20% of employees use platform
- ACV: 30 seats x $49 x 12 months = $17,640 (use $15K conservatively)
Bottom-Up TAM: 8,200 companies x $15,000 = $123 million
Note: This is narrower than top-down TAM because it focuses on a specific, validated ICP rather than the entire market.
Not all customers in your TAM are reachable with your current go-to-market capabilities. SAM narrows to customers you can actually target with your sales channels, marketing budget, and distribution model.
TAM: 8,200 companies x $15,000 = $123M
Reachability filters:
- Must use Slack (75% of tech companies) = 6,150 companies
- Headquartered in major metro areas (sales footprint) = 80% = 4,920 companies
Bottom-Up SAM: 4,920 companies x $15,000 = $73.8 million
SOM models realistic customer acquisition over 3-5 years based on your sales capacity, conversion rates, and competitive dynamics. This is where your market sizing connects directly to your revenue model.
SAM: 4,920 reachable companies x $15,000 = $73.8M
Sales capacity modeling:
- Year 1: 2 AEs, 50 deals each = 100 customers x $15K = $1.5M revenue
- Year 2: 5 AEs, 50 deals each = 250 customers x $15K = $3.75M revenue
- Year 3: 12 AEs, 60 deals each = 720 customers x $15K = $10.8M revenue
- Year 4: 25 AEs, 60 deals each = 1,500 customers x $15K = $22.5M revenue
- Year 5: 40 AEs, 65 deals each = 2,600 customers x $15K = $39M revenue
Bottom-Up SOM (Year 5): $39 million (53% of SAM)
This assumes 5% market share of SAM, aggressive but achievable with strong execution and $20M+ in funding.
VC market size expectations scale with funding stage. Pre-seed investors can work with smaller markets, but institutional Series A+ investors need billion-dollar TAMs to justify their fund economics. Understanding stage-appropriate market sizing prevents wasted pitches.
| Stage | Typical Raise | Minimum TAM | SOM Expectations |
|---|---|---|---|
| Pre-Seed / Angel | $250K - $1M | $100M+ TAM | Path to $5-10M revenue visible |
| Seed | $1M - $5M | $500M - $1B+ TAM | $20-50M revenue potential in 5 years |
| Series A | $8M - $25M | $1B - $5B+ TAM | $100M+ revenue potential, path to $1B valuation |
| Series B | $20M - $60M | $5B - $10B+ TAM | Clear path to $500M+ revenue, unicorn potential |
| Series C+ | $50M+ | $10B+ TAM | Path to $1B+ revenue, category leadership |
Key insight: VCs need your exit valuation to return their entire fund 1-3 times. A $500M fund needs $1.5B+ in total returns across their portfolio. Your outcome must be large enough to meaningfully contribute to that goal.
A typical $200M VC fund invests in 20-30 companies. With a 70% failure rate, only 6-9 companies will generate returns. To return 3x the fund ($600M), those winners must collectively generate $600M+ in exits. This means each winner needs to exit for $100M+, requiring markets large enough to support such outcomes.
Even a brilliantly executed company cannot generate $500M in revenue if the total market is only $300M. VCs invest in large markets first, great teams second - because execution can be coached, but market size is a hard constraint.
In a $10B market, you can pivot strategy, change ICP, or adjust business model while still having massive opportunity. In a $200M market, one strategic mistake can eliminate your TAM entirely. Large markets offer room for experimentation and iteration.
VCs strongly prefer markets growing at 20%+ CAGR. A growing market means you can gain customers even without taking share from competitors. In a flat or shrinking market, every customer must be taken from someone else - a much harder fight.
If your exit strategy is acquisition by strategic buyers (not IPO), smaller markets can work. A $200M market might be too small for VCs but perfect for a $50M acquisition by a strategic buyer seeking specific technology or customer relationships. In this case, position your market sizing around the strategic value, not just revenue potential.
Market sizing mistakes instantly destroy investor confidence. VCs see hundreds of pitches - they know the common errors and interpret them as signals that founders have not done the work. Avoid these mistakes to maintain credibility.
Claiming the largest possible market without meaningful segmentation. Classic example: "Healthcare is a $4 trillion market" for a diabetes monitoring app.
"The global healthcare market is $4 trillion. Even if we capture just 1%, that is $40 billion in revenue."
Why it fails: No segmentation, impossible claim, shows laziness.
"The US diabetes management market is $18B (ADA data). CGM devices represent $8B (40% of market). Our SAM is the 4.2M Type 1 diabetics x $1,200/year = $5B."
Why it works: Specific segmentation, credible sources, realistic scope.
Marketplace and platform businesses often show total transaction volume (GMV) instead of actual company revenue (take rate x GMV). This inflates market size by 10-20x.
Total freelance market (GMV): $1.5 trillion in annual freelance payments globally
Platform take rate: 10% average
Actual revenue TAM: $150 billion (not $1.5 trillion)
Always calculate revenue TAM for marketplaces, not transaction volume.
Stating market size numbers without explaining how you calculated them or what sources you used. VCs will immediately ask "where did you get that number?" - and if you cannot answer, your credibility evaporates.
"Our TAM is $12 billion."
Problem: No source, no methodology, impossible to validate.
"Our TAM is $12B (Gartner 2025). We calculated this as 500M global SMBs (World Bank) x 18% tech adoption (IDC) x $133 ARPU."
Why it works: Clear sources, specific calculation, easy to verify.
Claiming 10-20% market share without explaining how you will achieve that against entrenched competitors. In reality, capturing even 3-5% of a large market is extremely difficult and takes years.
Relying solely on analyst reports without validating with customer counts and unit economics. Top-down is easy but less credible than bottom-up customer-level math.
Top-down provides big-picture validation and shows you understand the broader category. Bottom-up proves you have counted real customers and understand unit economics. Use both and show they converge on similar numbers.
Red flag: If your top-down TAM is $5B but your bottom-up SAM is only $200M, investigate the discrepancy - one of your assumptions is wrong.
Citing market research from 2019-2020 (pre-pandemic) when market dynamics have fundamentally shifted. Always use data from the last 12-24 months.
Always validate that your market data reflects current reality, not pre-pandemic assumptions.
Showing global TAM when you only operate in one country, or claiming US market size when most of your customers are in Europe. Match your market geography to your actual GTM.
If you are US-only: Show US TAM/SAM/SOM, note global TAM in appendix for future expansion
If you are multi-region: Break down TAM by region showing your prioritization
If you are global from day one: Show global TAM but be prepared to explain GTM for each region
Calculating SOM as if you are the only player in the market. In reality, incumbents and funded competitors will capture most of the near-term market growth.
If there are 3 well-funded competitors in your space, you are fighting for a fraction of SOM - not the entire market. Acknowledge competitors and explain your differentiation that will help you capture your target share. VCs respect honest competitive analysis more than ignoring competition.
Your market sizing slide is typically slide 4-6 in your pitch deck. It should be visually clear, show nested circles, cite credible sources, and connect directly to your revenue projections. Here is exactly how to structure it.
Use concentric circles to show the relationship between TAM (outermost), SAM (middle), and SOM (innermost). This visual immediately communicates that you have a focused strategy within a large opportunity.
Example structure:
- Outer circle: "$45B Global TAM" (Gartner 2025)
- Middle circle: "$8B North America SMB SAM"
- Inner circle: "$240M SOM (3% share by Year 5)"
State exact numbers, not ranges. "$2.3B SAM" is better than "$2-3B SAM". Precision signals you have done detailed analysis.
Add footnotes showing your calculation approach and data sources. This prevents the inevitable "where did you get these numbers?" question.
Example footnote:
"TAM: Gartner CRM Market Report 2025 ($69.5B global) x 65% sales automation segment = $45B. SAM: US market (42%) x SMB segment (35%) x addressable categories (25%) = $8B. SOM: 575K companies x $4,200 ACV x 10% penetration = $240M Year 5 revenue."
Show where your revenue projection lands relative to SOM. If you are projecting $100M in revenue by Year 5, and your SOM is $250M, that implies 40% market share - which you need to justify.
Good example: "Our Year 5 revenue target of $75M represents 31% of our $240M SOM, achievable with 50 enterprise AEs closing 1,500 customers annually."
If your market is growing rapidly (15%+ CAGR), prominently feature this. Growing markets are far more attractive than flat or declining ones.
Example callout: "Growing at 22% CAGR (2025-2030)" next to TAM figure
When in doubt, use conservative numbers. VCs respect founders who under-promise and over-deliver. Better to surprise them with stronger traction than explain why you missed inflated projections.
Left side: Nested Circles Visual
TAM: $45B (outer circle, light amber)
SAM: $8B (middle circle, medium orange)
SOM: $240M (inner circle, dark orange)
Right side: Key Metrics
TAM: $45B - Global sales automation software (Gartner 2025, 18% CAGR)
SAM: $8B - North America SMB (10-500 employees) tech companies
SOM: $240M - Realistic Year 5 capture (3% of SAM)
Our Year 5 Target: $75M revenue (31% of SOM, 0.9% of SAM)
Bottom: Methodology Footnote
Sources: Gartner CRM Market Report 2025, Crunchbase company data, US Census Bureau business statistics. Bottom-up SAM validated via LinkedIn Sales Navigator (575K companies x $14K ACV = $8B).
Create detailed appendix slides showing your full top-down and bottom-up calculations. VCs often want to dig deeper on market sizing - having prepared backup slides shows thoroughness and lets you answer questions without fumbling.
New category creation is the hardest market sizing challenge. When Uber started, there was no "ride-sharing market" - only taxis and black cars. When Airbnb launched, "home-sharing" did not exist as a category. Here is how to size markets for new categories.
Identify what your product replaces or displaces, and size the spending on those existing solutions. Your TAM is some percentage of budget reallocation from old solutions to your new category.
Proxy markets (what Uber replaces):
- US taxi market: $11B annual revenue
- Black car/limo services: $8B annual revenue
- Personal car ownership (urban): $200B+ in costs (insurance, parking, maintenance)
- Public transit substitution: $15B in major metros
Conservative TAM: $30-50B (taxi + limo + partial car ownership substitution)
Actual market grew far larger as ride-sharing created new demand, but this provided defensible initial TAM.
Study how similar technologies or business models scaled when they were introduced. Use adoption curves from comparable innovations to project your market size.
Analogous markets for adoption curve:
- IDEs (Integrated Development Environments) took 10 years to reach 80% developer adoption
- Cloud infrastructure took 8 years to reach 50% enterprise adoption
- CI/CD tools took 6 years to reach 40% professional developer adoption
Market sizing approach: 28M global developers x 30% adoption (Year 5) x $20/month = $2B SOM
Use conservative adoption rates from analogous tools to project realistic capture timelines.
Survey your target customers about what they would pay for your solution. Combine responses with addressable customer counts to build bottom-up TAM.
Step 1: Survey 100+ ICP customers about willingness to pay
Step 2: Calculate average willingness to pay from survey (discount by 30-40% for survey bias)
Step 3: Multiply by total addressable customer count
Step 4: Apply realistic adoption curve (Year 1: 5%, Year 3: 15%, Year 5: 30%)
This approach is especially credible for B2B products where you can survey decision-makers directly.
Calculate the economic value your product creates for customers, and size the market based on value capture. If you save customers $10 for every $1 they pay you, the market is constrained by customer ROI tolerance.
Value created per customer:
- Saves 10 hours/week per sales rep (50 hours/month)
- Average rep fully loaded cost: $40/hour
- Monthly value per rep: 50 hours x $40 = $2,000
- Customers willing to pay up to 20% of value captured = $400/month per rep
TAM calculation: 5M sales reps in US x $400/month x 12 = $24B TAM
Value-based sizing ensures your pricing has room within customer ROI, making TAM more defensible.
For truly novel categories, acknowledge market sizing uncertainty while presenting your best estimates. VCs respect intellectual honesty more than false precision.
Framework: "This market does not exist today, so we have sized it using [proxy markets / analogous adoption curves / customer surveys]. Our conservative TAM is $X based on [methodology], though the market could be significantly larger if [adoption assumptions prove true]."
This shows you have thought rigorously about sizing while acknowledging the inherent uncertainty in new categories. VCs appreciate this honesty.
TAM (Top-Down): $9.4B enterprise collaboration software (Gartner 2014)
SAM (Bottom-Up): 15M knowledge workers in tech companies x $100 ARPU = $1.5B
SOM (Year 5): 500K paid users x $100 ARPU = $50M revenue (3.3% of SAM)
Result: Slack raised $120M Series B at $1.1B valuation. They exceeded projections, reaching $200M+ ARR by Year 5 and selling to Salesforce for $27.7B.
Key insight: Slack used conservative bottom-up SAM focused on tech companies only, even though their TAM encompassed all knowledge workers globally. This conservative approach built credibility with VCs.
TAM (Proxy Market): $280B global hotel industry + $85B vacation rentals = $365B
SAM (Addressable Segment): $85B vacation rentals + 20% hotel budget flexibility = $141B
Revenue TAM (10% take rate): $14.1B platform revenue opportunity
SOM (Year 5): $3B in bookings x 10% take rate = $300M revenue (2% of SAM)
Result: Airbnb raised $112M Series B. They massively exceeded projections, now generating $8B+ in annual revenue and valued at $75B+.
Key insight: Airbnb used proxy market sizing (hotels + vacation rentals) even though "home-sharing" did not exist as a category. They also correctly calculated revenue TAM (take rate x GMV), not GMV itself.
TAM (Payment Processing): $45B global payment processing revenue (Nilson Report 2012)
SAM (Developer-Focused): $8B online payment processing for SMB/developer segment
SOM (Year 5): $50B in payment volume x 2.5% blended rate = $1.25B revenue (15% of SAM)
Result: Stripe raised $18M Series A at $100M valuation. They far exceeded projections, now processing $1T+ annually in payments and valued at $95B peak.
Key insight: Stripe initially focused SAM on developer/SMB segment even though TAM was entire payment processing industry. As they proved product-market fit, they expanded SAM to include enterprise, growing much larger than initial SOM projections.
TAM (Video Conferencing): $4.1B enterprise video conferencing (Wainhouse Research 2013)
SAM (Cloud-Based SMB+): $1.8B cloud video conferencing (45% of market shifting to cloud)
SOM (Year 5): 200K business customers x $2,500 ACV = $500M revenue (28% of SAM)
Result: Zoom raised $30M Series B. Exceeded projections dramatically during pandemic, reaching $4B+ annual revenue and $100B+ peak valuation.
Key insight: Zoom focused SAM on cloud-based segment even though TAM included legacy on-premise systems. The pandemic massively expanded TAM beyond original projections, but their initial conservative sizing was credible and defensible.
TAM (Total Addressable Market) represents the entire revenue opportunity available if you achieved 100% market share with zero constraints. SAM (Serviceable Addressable Market) is the portion of TAM you can realistically target given your business model, product capabilities, and geographic reach. SOM (Serviceable Obtainable Market) is the realistic market share you can capture in the near term (typically 3-5 years) given competition, resources, and execution capabilities. For example: TAM might be a $50B global market, SAM might be $8B for your target segment, and SOM might be $400M representing 5% realistic market share.
The top-down approach starts with total market research from industry analysts: (1) Find total global market size from credible sources like Gartner, IDC, Forrester, or Statista. (2) Apply geographic filters based on your target markets (e.g., North America = 28% of global). (3) Apply customer segment filters based on your ICP (e.g., SMB = 40% of enterprise market). (4) Apply product category filters for your specific offering. Example: $500B global software market x 28% North America x 40% SMB x 30% productivity tools = $16.8B TAM.
The bottom-up approach builds from actual customer data: (1) Count your total addressable customers using census data, industry databases, or LinkedIn Sales Navigator. (2) Calculate your average revenue per customer (ARPC) based on pricing model. (3) Multiply: Total Customers x ARPC = TAM. Example: 500,000 US SMBs with 10-50 employees x $2,400 annual subscription = $1.2B TAM. For SAM, narrow to customers you can reach with your GTM strategy. For SOM, estimate realistic acquisition over 3-5 years based on conversion rates and sales capacity.
VC market size expectations scale with funding stage: Pre-seed/Angel: $100M+ TAM acceptable, focus on SOM potential. Seed: $500M-$1B+ TAM preferred, show path to $10-20M ARR. Series A: $1B-$5B+ TAM required, demonstrate $100M+ revenue potential. Series B+: $5B-$10B+ TAM expected, clear path to $1B+ outcome. The key is not just TAM size but demonstrating credible SOM capture - VCs want to see you can realistically build a $100M+ revenue company within your addressable market.
Common market sizing mistakes include: (1) Vanity TAM - using the largest possible market without realistic targeting (e.g., claiming all $5T of healthcare). (2) Confusing GMV with revenue - marketplace founders showing transaction volume instead of take rate revenue. (3) No methodology - stating numbers without explaining calculation sources. (4) Unrealistic SOM - claiming 10-20% market share with no competitive analysis. (5) Top-down only - not validating with bottom-up customer counts. (6) Using old data - citing pre-pandemic market research. (7) Geographic mismatch - global TAM when only operating in one country.
Present market sizing on a single dedicated slide: (1) Use nested circles visual showing TAM > SAM > SOM with dollar figures. (2) Show your methodology - cite sources for top-down, explain assumptions for bottom-up. (3) Include your 5-year revenue target positioned within SOM to show realistic capture. (4) Add a footnote with credible sources (Gartner, IDC, company filings, census data). (5) Use conservative numbers - investors will question inflated estimates. (6) Show market growth rate if expanding (CAGR). (7) Tie to your go-to-market strategy explaining how you will capture SOM.
Use both approaches and triangulate between them. Top-down provides big-picture validation from analyst reports, showing VCs you understand the broader market. Bottom-up provides customer-level specificity that proves you understand your ICP and unit economics. The most credible approach: start with top-down TAM from Gartner/IDC, then validate with bottom-up customer counting for SAM and SOM. If your bottom-up arrives at radically different numbers than top-down, investigate the discrepancy - it usually reveals flawed assumptions. Present both in your deck appendix.
For new categories, use proxy markets and substitution analysis: (1) Identify existing solutions your product replaces and their market size. (2) Calculate budget reallocation - what spending will shift to your category? (3) Use analogous markets - when Uber started, they referenced taxi/transportation spend. (4) Survey customer willingness to pay and extrapolate. (5) Model adoption curves from similar innovations. (6) Be conservative with timeline - new categories take 5-10 years to mature. Example: AI code assistants sized the market as percentage of developer salaries x productivity gain value, not as existing software spending.
Getting market sizing right is critical for fundraising. Use our free TAM SAM SOM calculator to model your market using both top-down and bottom-up approaches, validate your assumptions, and create investor-ready market sizing for your pitch deck.
Open Free TAM SAM SOM CalculatorTAM (Total Addressable Market) is the theoretical maximum if you achieved 100% market share globally
SAM (Serviceable Addressable Market) narrows to customers you can realistically target with your GTM strategy
SOM (Serviceable Obtainable Market) shows realistic near-term capture (3-5 years) given competition and resources
Use both top-down and bottom-up approaches and show they converge on similar market size
VCs expect $1B+ TAM for Series A and $5B+ TAM for Series B to justify fund economics
Avoid vanity TAM numbers - claiming the entire healthcare or education market instantly kills credibility
Cite credible sources like Gartner, IDC, Forrester, and show your calculation methodology
Conservative SOM is better than aggressive - VCs respect realistic projections over inflated claims
For new markets, use proxy market substitution and analogous adoption curves to size opportunity
Your SOM must support your revenue projections - if you project $100M Year 5 revenue, your SOM better be $200M+