TAM SAM SOM Calculator

A top-down market size is a multiplication of guesses, and the audience knows it. Population times price times two percentages produces a large number quickly, which is why it appears in so many pitch decks and why so few people believe it. Each factor is plausible on its own, but a 20% error in each compounds into a figure that could be off by half or double. Use this tool to frame the opportunity, then earn credibility by building the same number from the bottom up.

Bottom-up sizing starts from things you can count: named accounts in a target list, monthly leads by segment, realistic deal sizes, observed win rates, and how many reps or campaigns you can fund. It usually produces a smaller number than the top-down figure. That is fine. A defensible $40 million is worth more in a board meeting than an unexplained $2 billion, because every input can be challenged and survive.

Boards and investors read SOM, not TAM. TAM tells them whether the category is big enough to matter; SOM tells them whether your plan is achievable and what it implies for revenue in three to five years. They will compare your SOM to the revenue in your operating plan and to the market share incumbents actually hold. If SOM implies you will take a share no entrant in the category has ever won, the model fails regardless of how large the TAM looks. The 1%-of-SAM figure is here for the same reason: if it already exceeds your revenue plan, your ambition is not the constraint, execution is.