Market Sizing: The Test Most Founders Fail Before They Ever Start

A strategic plan can look impressive on paper and still be impossible to execute.

I’ve sat in planning meetings where revenue targets looked ambitious but completely achievable. Everyone around the table believed the business had a clear path forward. The projections made sense. The excitement was real.

Then we did one exercise.

We sized the market.

Suddenly the entire plan changed.

In more than one case, the business would have needed to capture somewhere between 40% and 60% of its entire addressable market just to hit the financial targets that had already been approved. Nobody had questioned the assumption because nobody had done the math.

That’s why market sizing isn’t an academic exercise. It’s one of the fastest ways to tell whether your strategy is grounded in reality or built on optimism.

We Don’t Have a Growth Problem. We Have an Assumption Problem.

Most founders begin with the number they want.

“We want to reach $50 million.”

“We want to double revenue.”

“We want to become the dominant player.”

There isn’t anything wrong with ambition. Every business needs it.

The problem starts when we work backward from the outcome we want instead of forward from the market that’s actually available.

Those are two very different planning processes.

One starts with desire.

The other starts with evidence.

Private equity firms don’t buy companies because the projections look exciting. They begin by asking whether the market can support the return they’re trying to achieve. If the market can’t support it, the investment thesis falls apart before the first dollar is invested.

Founders should do exactly the same thing.

Market Sizing Begins with Three Numbers

Every strategic plan should answer three questions before anyone discusses revenue targets.

Total Addressable Market (TAM)

Your Total Addressable Market is the total revenue opportunity if your business captured every possible customer.

Think of an HVAC contractor operating within a specific region.

The TAM is every dollar spent on HVAC installation and maintenance throughout that market, across residential and commercial customers.

Will you ever own all of it?

Of course not.

That isn’t the point.

TAM tells us whether the opportunity is large enough to justify the outcome we’re trying to build.

Serviceable Addressable Market (SAM)

The next number narrows the picture.

Your Serviceable Addressable Market is the portion of the market your business can actually serve.

If that same HVAC company only works on commercial properties within a limited geographic area, the available market becomes much smaller.

This is the market you’re actually competing for.

Many businesses unknowingly build financial models using TAM while operating inside SAM. That single mistake can make a growth plan appear far more realistic than it actually is.

The Number That Really Matters

The third number is where strategy becomes uncomfortable.

Your Serviceable Obtainable Market (SOM) represents the portion of your serviceable market you can realistically capture with your current resources, capabilities, and competitive position over the next three to five years.

This is where we stop talking about possibilities and start talking about probabilities.

Suppose your business currently holds 8% of its market.

Your financial plan requires reaching 40%.

That isn’t just a revenue target.

It’s a fivefold increase in market share.

Now we can ask better questions.

What has to be true for that to happen?

What capabilities must be built?

How much capital is required?

How many competitors would have to lose customers?

How long would that actually take?

Those are strategic questions.

The revenue target by itself isn’t.

The Financial Model Doesn’t Get the Final Vote

One of the biggest mistakes we make in planning is allowing the spreadsheet to dictate reality.

The spreadsheet says the business needs $100 million in revenue.

Fine.

Can the market actually support that?

If the answer is no, we don’t solve the problem by working harder.

We solve it by changing the assumptions.

Sometimes that means entering a larger market.

Sometimes it means expanding geographically.

Sometimes it means offering new services.

Sometimes it means acquiring another company.

And sometimes it simply means acknowledging that the original target was never realistic.

That isn’t failure.

That’s discipline.

Good Strategy Survives Contact with the Numbers

I’ve found that market sizing has a way of exposing weak strategies before they become expensive mistakes.

A plan that requires impossible market share isn’t ambitious.

It’s mathematically incompatible with the opportunity available.

That’s an important distinction.

We often think execution is where businesses fail.

Many times, they were already failing before execution ever began because the assumptions underneath the strategy were never tested.

The team simply spent the next three years trying to execute a plan that could never have worked.

Test the Market Before You Test Your Team

Before your next planning session, stop talking about revenue for a moment.

Start with three questions instead.

How large is the market?

How much of that market can we actually serve?

What percentage could we realistically win over the next three to five years?

Those answers don’t limit ambition.

They focus it.

The businesses that create extraordinary value don’t just dream bigger. They measure better. They test their assumptions before they commit resources. They make decisions based on evidence instead of enthusiasm.

Because once we ask the market to support our strategy, reality always gets a vote.

And reality is a far better place to discover a flaw than three years into a plan that was never possible to begin with.