Mon–Fri: 10:00 – 18:00 
Request a call 
TAM / SAM / SOM Calculator — Top-Down Market Sizing
Total Addressable Market, Serviceable Available Market, Serviceable Obtainable Market — in three layers with explicit geography, ICP, and realistic market-share filters. Built for founder decks and investor conversations.
TAM, SAM, SOM — and why most investor decks get this wrong
TAM, SAM, SOM are three concentric circles of market sizing. Get them wrong and your fundraise deck either looks naively huge (TAM = "$100B global market") or implausibly tiny (SOM = your current ARR). The right answer is somewhere in the middle, supported by explicit filtering math.
The three layers
- TAM (Total Addressable Market): total revenue opportunity if every potential customer bought from someone. Top-down: total companies in the world × average annual contract value. Bounded only by category, not geography or product fit.
- SAM (Serviceable Available Market): TAM filtered by what you CAN serve — geography, language, regulatory constraints, ideal customer profile. Usually 5-25% of TAM for B2B SaaS.
- SOM (Serviceable Obtainable Market): the slice of SAM you can realistically win in 3-5 years given competition, sales motion, and execution speed. Usually 0.5-5% of SAM.
The formulas
TAM = total companies × avg ACV SAM = TAM × geography filter × ICP filter SOM = SAM × realistic market share (3-5 years) customers at SOM = SOM / avg ACV
What investors actually want from a TAM-SAM-SOM slide
Not a $50B TAM number. They want to see that you have thought through who you can and cannot serve, and what a realistic 3-5 year share looks like. A $1B SAM with 2% SOM ($20M ARR) reads as more credible than a $50B TAM with hand-waved capture.
Common mistakes
- "1% of a huge market" — investors trained to spot this. 1% of a $100B market is still $1B, which is a 100x growth target from $10M ARR. Implausible.
- Ignoring geography: "We can sell globally" almost always means "in 5 years maybe". Apply geo filter realistically (US-first, then 5-7 countries that match GTM motion).
- Skipping ICP filter: Even within geography, not every company fits the ICP. Filter by company size, industry, tech stack maturity.
- Top-down only: Pair top-down with bottom-up (current ARR × growth rate × years). The two methods should triangulate within 2-3x of each other. If they do not, one is wrong.
How to size your market in three layers
Five inputs. Two layers of filtering. One credible SOM.
Count total addressable companies
Use industry data: Statista, Crunchbase, government registries. If you target "B2B SaaS companies with 50-500 employees", count those globally first.
Estimate avg annual contract value
From your actual closed-won deals (last 90 days). Use median if you have a few outliers; mean if distribution is normal.
Apply geography filter
What % of the global market are you ACTUALLY going to sell into? US-only: 35%. US + EU: 55%. English-speaking world: 65%. Be honest about GTM motion.
Apply ICP filter
Within geography, what % match your ICP? Company size + industry + tech maturity + budget. Usually 15-30%.
Set realistic 3-5y market share
For most early-stage startups: 1-3% within 3-5 years is defensible. 5%+ requires either a hot category or proven traction. Use lower end for fundraise deck.
Frequently asked questions about market sizing
TAM = total companies × avg ACV. SAM = TAM × geography filter × ICP filter. SOM = SAM × realistic 3-5 year market share. This calculator does the top-down version; pair with bottom-up (current ARR × growth × years) for triangulation.
TAM = total revenue opportunity if everyone bought. SAM = the slice you CAN serve given geography + ICP. SOM = the slice you can REALISTICALLY win in 3-5 years given competition + execution. TAM is biggest; SOM is most defensible.
1-3% in 3-5 years is defensible for most early-stage B2B SaaS. 5%+ requires either a fresh category (no entrenched competition) or already-proven traction. Anything above 10% usually fails the smell test.
Both, then triangulate. Top-down: this calculator (total market × filters). Bottom-up: current ARR × growth rate^years. If the two numbers are within 2-3x of each other, you have a credible SOM. If they differ by 10x, one method has bad inputs.
Build proxy data: count companies on LinkedIn matching your ICP × estimated ACV from your own deals. Or use peer comparables — find a public competitor and use their reported customer count and ARPC. Show your work in the deck so investors trust the SOM.
For seed: $1B+ TAM is the soft minimum, $5B+ for outlier rounds. Series A: typically $10B+ TAM. Series B+: $20B+ TAM. But what matters more is a credible path to $100M+ ARR — which depends on SOM, not TAM.
