Tool

Market Sizing: Formula and Calculator

Wall Street Prep Free Intermediate

A finance-grade reference for the actual formulas, with a calculator so you can sanity-check your TAM, SAM, and SOM arithmetic. It is more rigorous than the marketing blogs and useful when you want the math laid out cleanly. Handy as a cross-check against your own model.

  • Clear formulas for each of the three market layers
  • A calculator to verify your arithmetic quickly
  • A more rigorous, finance-oriented framing than typical blogs
Open on wallstreetprep.com ↗

It answers 2 questions

  1. What are TAM, SAM, and SOM and how do I actually calculate them?
  2. How do I size a market for India specifically when data is messy?

Read with it

  1. The single best thing ever written on customer conversations. It teaches you to ask about the customer's life and past... momtestbook.com Book · ~130 pages The Mom Test Rob Fitzpatrick
  2. Most market sizing advice online is generic TAM SAM SOM filler. This one is written by an investor, backed by a survey of 30... Pear VC Essay · ~15 min read Market Sizing Guide Ian Taylor
  3. When there is no category report to point at, you have to build the number yourself, and this is the essay that teaches you... Andreessen Horowitz Essay · ~20 min read 16 More Startup Metrics Anu Hariharan, Frank Chen, Jeff Jordan
  4. Blume's annual report is the single best data-grounded read on what is actually happening in Indian internet and consumption,... Blume Ventures Article · ~180 charts Indus Valley Annual Report 2025 Sajith Pai, Anurag Pagaria and team (Blume Ventures)
  5. Video · ~50 min How to Evaluate Startup Ideas Kevin Hale, Y Combinator
  6. Before you sweat which side to seed, Gurley helps you judge whether your marketplace is even structurally worth building. He... Above the Crowd Essay · 20 min read All Markets Are Not Created Equal: 10 Factors to Consider When Evaluating Digital Marketplaces Bill Gurley
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