How to Estimate Market Size

A startup’s potential scale is bound by the size of its target market. One of the first questions investors ask is: “What is your market size?” Understanding and communicating your market size demonstrates that you are targeting a large opportunity and that you understand it deeply.

Key Takeaways

• Big companies can only exist in big markets.
• Use a bottom-up approach to estimate market size: multiply the number of customers by average revenue per customer per year.
• Present your total addressable market (TAM) and projected revenue for 5+ years.
• Market sizing is a rough estimation, clarity and ambition matter more than precise numbers.

1. Why Market Size Matters

If you want to create a company with a DoorDash-sized impact, you need a large market. Investors want to see that your startup can generate hundreds of millions of dollars in high-margin revenue within the next decade.

2. How to Estimate Market Size

The bottom-up approach is the most reliable. It uses real assumptions grounded in your business model and is testable by investors.

Steps:

• Identify target customers
• Estimate average revenue per customer per year
• Multiply to calculate market size

Bottom-Up vs. Top-Down

Keep it simple, complex calculations do not add credibility early on.

3. What is Market Size?

Rather than focusing on jargon like TAM, SAM, or SOM, focus on:

• Total Addressable Market (TAM) – the total revenue opportunity if your company captured 100% of the relevant market.
• Projected Revenue (5+ years) – realistic revenue estimates based on a bottom-up calculation.

Presenting Incremental Market Expansion

This method communicates growth potential clearly, without overcomplicating or relying on untested assumptions.

4. When to Estimate Market Size

• Estimate for 5+ years into the future. For long-term trends, consider 7–10 years.
• If the market is growing rapidly, also present current market size alongside future projections.
• This demonstrates that you understand both the existing and emerging opportunity.

5. Building Your Market Size Assumptions

Step 1: Number of Customers

Define target customers

Focus on the segment that contributes most revenue.

Example:

• Broader market: all US residents
• Convincing segment: 25–40-year-olds who eat out weekly

Estimate total customers

Sources vary by business type:

Estimate customers captured in 5 years

• Consider customer acquisition and retention per year
• Compare with market share of dominant competitors
• Factor in network effects, distribution, and market fragmentation

Example calculation:

Step 2: Average Revenue per Customer per Year

Choose revenue model

Focus on the core revenue stream. Examples:

Estimate transaction volume

Understand customer behavior: how often they will use the product or service.

Estimate pricing

Examples by business category:

Step 3: Calculate Market Size

Multiply # of customers × average revenue per customer.

Adjust assumptions iteratively to align with your overall vision and long-term growth.

6. Additional Tips

• Think long-term: Estimate potential demand 5–10 years out.
• Focus geographically: If starting in one country, present addressable market there first.
• Use annual revenue: Avoid inflating numbers.
• Include take rate for marketplaces or fees for financial products.
• Leverage S-1 filings of public companies to validate assumptions and projections.

Template:

Example: