1. The Revenue Ceiling
TL;DR > Market size is the absolute revenue ceiling of your company. If you capture 100% of a tiny market, you still have a tiny company.
Investors ask for market size not because they believe your specific numbers, but because they want to know how you think about scale. If your market is only $10M, even a monopoly won't generate venture returns.
$100M
The Revenue Target
Most venture capitalists require a market size large enough for your startup to realistically hit $100M in Annual Recurring Revenue (ARR) within 7-10 years.
2. Top-Down vs. Bottom-Up
There are two ways to calculate market size:
Top-Down: Taking a massive industry figure and claiming 1% of it. (e.g., "The AI market is $500B. If we get 1%, we are a $5B company.") *Investors hate this.* It ignores distribution and pricing reality.
Bottom-Up: Multiplying your expected number of customers by your average annual price. (e.g., "There are 50,000 dental clinics in the US. We charge $2,000/year. Our market size is $100M.") *Investors love this.*
Top-Down vs Bottom-Up Accuracy
Why Bottom-Up modeling is significantly closer to reality.
3. The Formula
To dive deeper into the specific acronyms investors use to measure these markets, read our comprehensive guide on TAM vs SAM vs SOM.