How to Calculate TAM, SAM and SOM: A Worked Example

TAM, SAM and SOM are three nested layers of market size. TAM is everything your product could serve in theory. SAM is the part your current product and channels can actually reach. SOM is the share you can realistically win in the next few years. To calculate them, set the frame top-down, then check it bottom-up with customers multiplied by annual spend. When the two approaches agree, your market slide will hold up under questioning.

What TAM, SAM and SOM mean

Each layer narrows the one above it. Investors read TAM for the ceiling, SAM for your focus, and SOM for whether your plan is realistic.

Two methods: top-down and bottom-up

Top-down starts from an industry total and filters by customer type, region and price band. It is fast and the data is easy to find. The weakness is that you inherit someone else's definitions and guess at the filters. One question, "where does this 60% come from?", can stall you.

Bottom-up starts from a single customer: number of target customers multiplied by what each spends per year, or by your price. Every number can be broken down and tied directly to your business model. The catch is that you need reliable data on customer counts and spend.

Do both. Use top-down to set the frame and bottom-up to test it. If the two results are far apart, one of your assumptions is wrong.

A full worked example

Here is the complete calculation for FreshSource, a restaurant supply startup in our example gallery. Industry figures come from that example's input. Ratios marked as assumptions exist only to demonstrate the method; replace them with data you have verified.

1. Start with the industry total. The example puts China's restaurant ingredient purchasing at roughly RMB 2.5 trillion. This is not yet the TAM.
2. Narrow to TAM. The product serves small and mid-sized restaurants; large chains usually run their own supply chains. Smaller outlets account for about 60%, so TAM is around RMB 1.5 trillion. Many decks present the full RMB 2.5 trillion as TAM, a common overstatement.
3. Narrow to SAM. The company launches in five cities in East China, where the example's input estimates the serviceable market at about RMB 120 billion. That is the SAM.
4. Check SAM bottom-up. Average purchasing per restaurant is RMB 32,000 a month, or about RMB 384,000 a year. RMB 120 billion divided by RMB 384,000 is roughly 312,000 restaurants. Now verify: do those five cities really have around 300,000 small restaurants? If the real count is 150,000, your SAM is about twice what it should be.
5. Estimate SOM. Assume the company reaches 2% of SAM's restaurants within three years (an illustrative assumption): about 6,250 restaurants, or roughly RMB 2.4 billion in GMV.
6. Convert GMV to revenue. At the midpoint of a 3 to 5% commission, 4%, that is about RMB 96 million. Add the SaaS fee of RMB 999 per restaurant per year across 6,250 restaurants, about RMB 6.2 million. SOM revenue is around RMB 100 million a year.
7. Test SOM against sales capacity. The company reached 1,200 restaurants in its first 10 months, about 120 a month. Hitting 6,250 in three years requires about 140 a month: a bit faster than today, which is plausible with the expansion the round funds. If the math demanded 1,000 new restaurants a month, SOM would need to come down.

Put the full calculation in the appendix and keep only the conclusions and key definitions on the market slide. When investors probe, you can unpack any layer.

Sanity checks that survive questions

• Compare two sources. The industry report total and your bottom-up result should be in the same range.
• Check customer counts. Your implied number of customers should match public business registrations or store counts in order of magnitude.
• Check price. Your average contract value should come from closed deals, not quotes.
• Add growth. Show how fast the market is growing, with source and year.

Five common mistakes

Laying out the market slide

The usual layout is three concentric circles or a three-step funnel, with one line of definition next to each layer, for example "small restaurants in five East China cities, about 312,000 times RMB 384,000 a year." Make the headline a conclusion: "Our five launch cities are a RMB 120B serviceable market." Keep the detailed math in the appendix.

For where the market slide sits in the overall storyline, see our pitch deck structure guide. Questions about market size tend to be specific, so review our checklist of questions investors ask before your meetings.

Building the market slide with AI

When you give our AI slide studio a business plan with market data, the generated pitch deck includes a dedicated market size slide. If your source does not explain how SAM or SOM was derived, that spot is marked [TBD] instead of being filled with an invented figure. See the full input and output in the FreshSource pre-Series A example, then upload your own plan in the pitch deck generator.

FAQ

Where do I find data for TAM, SAM and SOM?

Common sources include government statistics, industry association reports, annual reports and IPO filings of listed companies, analyst research, and your own customer research. Cite the source and year, and when sources use different definitions, pick one and stay consistent.

What share of SAM should SOM be?

There is no fixed ratio. SOM should come from your sales capacity, built bottom-up: how many customers your team can reach, your conversion rate and your average contract value. If the result looks high, be ready to explain why.

Is a bigger market size always better?

No. A huge number that is only loosely tied to your product suggests you have not focused on a target customer. Investors care more about whether your SAM and SOM are credible and whether the market is growing.

A market slide persuades through its reasoning, not its size. Work through the three layers, verify them, and you will be able to take any question apart calmly.