TAM SAM SOM Calculator
Build a credible market size in 60 seconds. Switch between bottom-up and top-down, and get a verdict on whether your numbers will survive an investor pitch.
Inputs
Pick a method. Bottom-up is more credible to investors. Top-down is faster.
Total count of qualified buyers (e.g. SMBs in your category)
Realistic ACV at maturity, not freemium price
Geography, language, regulation, channel filter
Realistic 5-year share, typically 1 to 5%
Investor market-sizing benchmarks
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Frequently asked questions
What is TAM SAM SOM?+
TAM, SAM, and SOM are three layers of market sizing. TAM (Total Addressable Market) is the total revenue opportunity if you captured every possible customer worldwide with no competition. SAM (Serviceable Available Market) is the slice of TAM your product can actually reach given geography, language, regulation, and channel. SOM (Serviceable Obtainable Market) is the realistic share of SAM you can win in the next 3 to 5 years. Investors expect founders to walk through all three levels in a pitch deck.
Should I use top-down or bottom-up TAM?+
Use both and compare them. Top-down starts from analyst reports (Gartner, IDC, Statista) and applies your slice of that broader market. Bottom-up multiplies your target customer count by your expected revenue per customer. Top-down is fast but often inflated. Bottom-up is more credible and shows investors you understand unit economics. The strongest pitches present a bottom-up number and validate it against a top-down ceiling.
How do investors actually evaluate market size?+
Most VCs apply a credibility filter. If your TAM is over $50B, they discount it heavily because the assumptions are usually too loose. If your SOM in year 3 is below $20M ARR for a venture-scale outcome, they pass. The sweet spot is a TAM of $5B to $50B, a SAM that is at least $1B, and a credible 5-year SOM of $50M to $200M ARR. Anything outside that band invites either skepticism (too small) or skepticism (too big to be real).
What is a realistic market share for a startup?+
For an early-stage startup, a credible 5-year SOM is 1 to 5 percent of your SAM. Best-in-class category leaders eventually hit 10 to 20 percent of their SAM after a decade, but assuming you hit those numbers in year 3 is a red flag. If your business model has strong network effects or winner-takes-most dynamics (marketplaces, social, payments), you can credibly model higher share. For pure SaaS, plan on a long, fragmented road.
What is the difference between TAM and market cap?+
TAM is annual revenue available in the market. Market cap is the equity value of a single public company. These are not interchangeable. A market with $20B TAM might contain ten public companies with a combined market cap of $200B, because public market multiples are typically 5x to 15x revenue. When investors ask about market size, they want annual revenue (TAM) not the combined valuation of incumbents.
How do I size a market that does not exist yet?+
For genuinely new categories, work bottom-up from analogous markets and adjacent budgets. If you are building AI agents for customer support, your TAM is not "the AI agent market" (which barely exists yet). It is the existing customer support software market plus the existing BPO labor market, since those are the two budgets you replace. Anchoring on existing budgets is much more credible than projecting a hypothetical new category.
How do you defend a SOM in a pitch deck?+
Three things: (1) Show your go-to-market math. If you can convert 2 percent of qualified leads at $10K ACV and you can reach 100K qualified leads, your year-3 SOM is roughly $20M ARR. (2) Anchor to comparable companies at the same stage. If a competitor hit $50M ARR in 4 years from a similar starting point, your $30M target is defensible. (3) Reveal your assumptions transparently. The number itself matters less than whether your reasoning survives scrutiny.