Free calculator · Venture & Startup Finance
TAM / SAM / SOM, Bottom-Up Market Sizing
Sizes a market bottom-up into TAM, SAM, and SOM dollar figures from unit counts and contract value rather than top-down percentages. Inputs are total units in the market, serviceable units, reachable units near-term, expected penetration, and annual contract value.
By Devon Coombs, CPA, MBA · Teaching Professor of Finance, Santa Clara University · Reviewed August 2026
From the author: Devon Coombs, CPA, MBA teaches finance at Santa Clara University and works with corporate teams on practical AI.
AI training for finance teams · Consulting · The 10 Laws of Finance
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TAM / SAM / SOM, Bottom-Up Market Sizing
TAM · total ceiling
$2.70B
SAM · what the model can serve
$432.0M
SOM · realistic near-term
$2.4M
675 units × $3,600 ACV
TAM ÷ SOM gap
~1,111×
a factor-of-1,000 gap is normal and honest
Credible sizing is bottom-up: filter the market to firms that would pay, in reachable geographies, at the real price. A founder who pitches the broadest TAM as the opportunity loses credibility; the SOM with a clear expansion path is the story investors underwrite.
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This calculator comes from the free Entrepreneurial Finance course, where the concept is taught with readings, worked examples, and practice questions.
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Built by Devon Coombs, CPA, MBA, Teaching Professor of Finance at Santa Clara University.