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Market size: what it means and how to read an estimate
Market size is how much a market is worth to the businesses in it: the number of buyers times what each pays in a year. An estimate is only useful when it says exactly what it counts. For a market that buyers search for, size also shows up as the US monthly searches for what the market sells.
What market size means
A single "market size" number hides three different questions. Estimates often blur them.
Say a service costs $1,200 a year per business. Here is how the same market reads at each layer.
| Layer | What it counts | Say |
|---|---|---|
| Total addressable market | All the businesses that could buy the service | 100,000 businesses x $1,200 = $120 million |
| Serviceable market | The ones you can reach with your offer, in the places you serve | 20,000 businesses x $1,200 = $24 million |
| Obtainable share | What you can win in the next year or two | 200 businesses x $1,200 = $240,000 |
The first number is the one often shown in pitch decks. The third is the one you plan around. A quoted market size that stops at the first row tells you very little about your own market.
The arithmetic behind a market size estimate
Behind every figure there is a multiplication: buyers times spend per buyer. That covers the questions people type as "how to calculate market size" and "how to work out market size". The arithmetic is short. Everything depends on whether the two numbers are believable.
There are two ways to read an estimate. A top-down estimate starts from a large published total and takes a share of it. A bottom-up estimate starts from the number of buyers and what each pays. A good estimate gives both, and the two land close together.
Take an example with round numbers, labelled as one.
| Route | Say | Result |
|---|---|---|
| Top-down | A $100 billion industry, a trade that is 4% of it, a region that is 2% of the country | $80 million |
| Bottom-up | 1,000 firms in the region, each spending $90,000 a year on this | $90 million |
Both land near $85 million, so the estimate holds. If one said $8 million and the other $80 million, one input is wrong, and you would stop before you spent anything on it.
Market size in searches
Searches give a second way to size a market. A search is a person saying what they want, and the US monthly searches for what a market sells are a count of how many people are asking, month after month. They are not revenue. They are numbers you can trace to a page, row by row, which a top-down figure cannot offer.
The count has a catch: not every search comes from a buyer. In freight factoring, a B2B finance service, one count of the US market covered about 309,080 searches a month, and 272 of its 1,569 searches, about 24,460 a month, looked relevant but came from the wrong audience (the counts are set out under negative keywords for search ads). So the market an ad account pays for is bigger than the market a business can sell into. A size that includes the wrong audience is a size you will never collect. Read US monthly search volume for how to treat a single number.
How to read a market size estimate
Ask four questions of any figure you are shown.
- What does it count? Buyers, revenue or searches. They are not the same, and one cannot stand in for another.
- Which layer is it? Total, serviceable or obtainable. If the page does not say, assume the biggest.
- Which country and which period? A US monthly figure and a global yearly one cannot be compared.
- Can you trace it? A number with a link behind it can be checked. A number without one is a claim.
Mistakes in market estimation
- "We only need 1%." One percent of a huge total is still a made-up share until you can name who the 1% are.
- Mixing layers. The total from one row and the share from another give a number that belongs to no market.
- Counting the wrong audience as demand. Searches from people who will never buy raise the size and lower your return.
- Counting one need twice. The same need listed twice makes the market look bigger than it is.
- Trusting the output of a calculator. A market size calculator multiplies the two numbers you give it. It cannot tell you whether they are right.
What to do with a market size
A size is only useful if it changes a decision.
- Set a ceiling. No ad budget or content plan should cost more than the serviceable part of the market can return.
- Choose between markets. Compare serviceable sizes, not totals.
- Remove the wrong audience first. Cut those searches before you size or bid, so the number you plan around is one you can sell into.
- Find where to start. Look at which needs the leading competitors do not cover, and build one page for each. Competitor gap analysis shows how to read that list.
When a provider quotes you a market size, ask what the number counts and whether each row links to a page you can open.
FAQ
How do I calculate market size?
Multiply buyers by what each pays in a year. Then do it again from the other direction, starting from a larger total and taking a share. If the two answers land close together, the estimate holds up.
Is there a market size calculator?
Calculators exist, and they all do the same multiplication. They return whatever you feed them, so the answer is only as good as the two inputs. Treat the output as a rough figure, not a fact.
What is a market size estimate?
It is a figure for how many buyers a market has, or how much they spend, with a layer attached: total, serviceable or obtainable. An estimate that does not name its layer cannot be compared with another.
Where to go next
Go back to market analysis for size, demand and landscape together. To see a market counted with a link behind every row, open a sample report. If you run a lead business, market counts for lead generation shows what that buyer gets.
Checked by a person and delivered within 24 hours, with a link and a search number behind every row.