Market Sizing: How to Estimate How Many Customers Want Your SaaS

Every founder gets asked the same question in the first investor or advisor call: "How big is the market?" If you answer with a hand-wave, you lose credibility. If you answer with a number you made up, you lose your own money when you build for a market that isn't there.

The good news: you don't need to commission a research firm. The demand is already sitting in public, in people's own words, on social media. You just need a method to count it. Here's a repeatable, defensible way to estimate your SaaS market size from social demand signals — before you write a single line of code.

Step 1: Define the buyer, not the tool

Most people size a market by the tool category ("CRM market is $60B"). That's useless for a founder, because the number is built from what big companies already spent, not what your buyer needs.

Instead, define the person:

• Who has the problem?
• Where do they hang out online?
• How do they describe the problem in their own words?

Write down 5–10 natural-language phrases your buyer would actually type or post. "I waste hours reconciling spreadsheets" beats "expense management." You're going to search for these phrases, so they need to sound like a person, not a product manager.

Step 2: Count demand posts per month

Now search each phrase across the public social feeds where your buyer lives (Bluesky, X, LinkedIn, Reddit, niche forums). For each phrase, count how many times it appeared in the last 30 days. Be strict: only count people who have the problem, not vendors selling the solution.

Let's say you find 300 genuine demand posts in a month across a handful of phrases. That's your raw signal count.

Step 3: Apply the visibility multiplier

Here's the key insight most people miss: the posts you see are a small fraction of the total market. For every person who publicly complains, many more silently have the problem. Research on help-seeking behavior consistently shows that only a fraction of people who have a problem ever post about it publicly.

A defensible range is a 20x–100x multiplier between public posts and the total addressable population. So:

• 300 posts/month × 20x (conservative) = 6,000 people/month with the problem
• 300 posts/month × 100x (optimistic) = 30,000 people/month

That's the population actively feeling the pain right now. The total addressable market is larger — it includes people who will develop the problem over time — but this active number is the one that matters for whether you should build.

Step 4: Discount by buying intent

Having the problem isn't the same as being willing to pay. Apply a second discount for intent:

• If people are just complaining (no search for a solution) → 5–10% will buy
• If people are searching for a tool → 15–30% will buy
• If people are paying for a workaround → 30–50% will buy

Take the conservative market: 6,000 people/month, and assume the posts skew toward "searching for a tool," so ~20% buy. That's 1,200 potential buyers per month. Even at a $20/month product with a 2% conversion on your landing page, that's a real, defensible business — and it tells you the ceiling before you build.

Step 5: Sanity-check against your funnel

The whole point of this exercise isn't to predict the future perfectly — it's to give you a number you can check against reality as you go. Once you have a landing page, your actual traffic, signups, and waitlist are real-world validation of the estimate.

• If your traffic massively exceeds what the estimate implied, the market is bigger than you thought — raise prices or expand scope.
• If you can't generate any traffic in a niche the estimate said was large, your problem phrasing or channel is wrong — refine and retest before blaming the market.

The estimate is a hypothesis. Your funnel is the experiment. Together they tell you the truth.

The takeaway

You don't need a $10,000 market research report to know whether your SaaS idea is big enough. Count the demand posts in a month, apply a conservative visibility multiplier, discount by buying intent, and you have a defensible, numbers-based market size — built entirely from what real people are saying publicly.

Then the real work begins: building a landing page, driving traffic, and letting actual signups either confirm or correct your estimate. Market size isn't something you guess once. It's something you measure, refine, and grow.