Where we start
The Business track is for the people who ask for a market size and the people who will be judged on what it says: the marketing lead, the BD lead, the founder, the head of data in the room. Four sessions: tonight, what a size is for; then how to read a sizing deck without being dazzled; then who owns which half of the work; then how to get from a size to a plan you can defend. No code. The Analyst track builds the same numbers by hand and in the browser. Kettle & Co, a direct-to-consumer tea brand, is constructed: its people, plans and pilot numbers are invented and labelled. The Japanese households and their tea spend are real, read from the Statistics Bureau of Japan.
★ What you walk out with tonight. One sentence that ties a sizing request to the decision it informs, a clear picture of which of TAM, SAM and SOM that decision actually needs, and a category choice written down before the first number, with its reason. That sentence becomes the top line of the sizing brief in Business session 3.
A size answers a decision, not a curiosity
5 min liveA market size is evidence. Evidence is for a decision: enter or not, how much to spend, which segment first, how many people to hire. If nobody can say which decision the size feeds and which value of it would change the decision, the work will be done twice: once to produce a number, and again when somebody asks what it means.
LiveThree decisions a size can serve, and what each needs3 min▶
Go or no-go. "Should we enter at all?" needs a range and a threshold. If the whole range sits above the line the business set, the answer is yes whatever the exact number. If it straddles the line, the answer is "measure the input that moves it most", which is Analyst session 4.
How much to spend. "How big a team, how much media?" needs the part of the market the company can realistically reach in the next two or three years, not the whole market. A budget sized to the whole market is how a plan ends up hiring for a share it will never win.
Which segment first. "Japan or Korea, households or offices?" needs two sizes built the same way, so the comparison is fair. Two numbers from two different methods, or two different reports, compare the methods as much as the markets.
Self-studyWhy "just a ballpark" still needs the decision2 min▶
A ballpark is a range with a wide band. It is still useful, as long as somebody knows which threshold the band is being compared with. "Somewhere between 10 and 30 billion yen" decides a go or no-go if the line is at 5, and decides nothing if the line is at 20. Asking for the threshold is not bureaucracy; it is how an analyst knows when to stop measuring.
The number that arrived without a question. Kettle & Co's BD lead asks for "the Japan market size" for a board pack. The data team returns a figure for all tea bought by Japanese households, the board likes it, and three weeks later the marketing lead asks how many people to hire for Japan. The board figure cannot answer that: it includes bottled tea drinks sold in every convenience store, which Kettle does not sell. The sizing is redone from scratch with a decision attached. Constructed Kettle & Co example; the shape is common.
Three sizes, and why the biggest is the least useful
5 min liveTAM, total addressable market, is everything the category could sell if every possible buyer bought. SAM, serviceable addressable market, is the part your product, price and channel can actually serve. SOM, serviceable obtainable market, is the part you can realistically win in a stated time. All three are definitions, not measurements: each one is only as good as the line drawn around it.
LiveWhere the three numbers come from3 min▶
TAM, 198.24 billion yen a year. 34,553,907 two-or-more-person households in the 2020 Census, times 5,737 yen a year that the average such household spends on green, black and other leaf tea in the Family Income and Expenditure Survey (2023-2025 average). Both inputs are real. It is the bench's "every tea drinker is our customer" rung.
SAM, 19.63 billion yen a year. The same households and spend, times two constructed Kettle & Co assumptions: a third of leaf spend is premium (0.33), and three in ten of those purchases happen online (0.30). The household count and the survey spend stay real; the shares are planning assumptions the Analyst track turns into ranges.
SOM, 1.96 billion yen a year. Kettle & Co's own constructed year-5 plan: 10 percent of SAM. Whether 10 percent is realistic is a separate question, and Business session 4 and Analyst session 5 treat it as one.
Every number here is printed by the bench in Analyst session 6. Your numbers will differ as soon as you change an assumption there.
Self-studyWhy TAM still appears on every deck2 min▶
TAM is the number that makes a room lean forward, and it is the hardest to argue with, because it is mostly real statistics. The weakness is not that it is wrong. It is that it answers "how big is the category", which nobody in the room has to decide. Keep it on the slide as context, one line, and put the decision against SAM and SOM.
The category is chosen before the size
5 min liveBefore TAM, SAM or SOM, somebody decides what market this is. "Tea", "premium loose-leaf" and "wellness drinks" are three honest descriptions of what Kettle & Co sells, and they produce three sizes from the same survey and the same households. Choosing between them is not an analyst's call. It is a positioning choice: which frame makes Kettle's value obvious to the buyers it wants. Marketing makes it, on purpose, and writes it down.
LiveCategory last in positioning, category first in sizing3 min▶
April Dunford's positioning method, as summarised in her book Obviously Awesome (reported here from secondary summaries, not quoted), works in a fixed order: start from the competitive alternatives a buyer would use if you did not exist, then the attributes only you have, the value those attributes create, the buyers who care most about that value, and only then the market category, chosen as the frame that makes the value obvious.
That order matters for sizing. The category is the output of positioning, and it is the input to sizing. If Kettle positions against supermarket tea bags, "tea" is the frame and the market is enormous and crowded. If it positions against specialist tea shops for people who brew leaf at home, "premium loose-leaf" is the frame, the market is smaller and the plan is believable. Sizing cannot choose for marketing. It can show marketing what each choice implies.
The positioning work itself belongs to marketing and is taught in Marketing, session 2 ↗. Strategy frameworks around the choice live in Strategic Thinking ↗.
Self-studyWhy the wellness frame is tempting, and what it costs2 min▶
The wellness drinks frame adds mineral water, sports drinks and lactic acid drinks to tea. It is 271.00 billion yen at the middle, the biggest number on the page, and it is defensible on a slide: tea is a wellness drink. The cost shows up the moment anyone builds the bottom-up. Kettle's pilot customers buy leaf tea; none of them told Kettle they were choosing between leaf tea and a sports drink. The gap between the two methods widens to 20.75x, and no single input inside its range can close it, because the two methods are now sizing different things.
The office tea question. Kettle's BD lead also wants to know how big "the B2B office tea market" is. That is a category choice too, and a harder one: offices buy tea through suppliers, in bulk, often bundled with coffee and water, and no household survey sees it. Before anyone sizes it, BD has to say what Kettle would sell to an office and instead of what. Analyst session 3 shows how to size a market when no official table measures it. Constructed example.
Write the sizing question before the number
★ 22 min · everyone works it throughNo code, just a page. Take one sizing request you have received or are about to send, or use Kettle & Co's "how big is Japan for us?". Five steps turn it into a question an analyst can answer and a leader can act on. Do step 1 together, steps 2 to 4 alone or in pairs, then read your step 5 sentences aloud. Your answers will differ from Kettle's, and that is the point.
Step 1 · Name the decision. One line, a verb and a date. "Understand Japan" is not a decision; "enter Japan online next year, yes or no" is. If you cannot name it, stop and ask the requester. That conversation is the most valuable ten minutes of the whole sizing.
Step 2 · Write the threshold. Which value of the size would change the decision? Ask the owner for it in their language: the revenue that would justify a team, the size below which the market is not worth the distraction. A rough threshold is fine; no threshold is not.
Step 3 · Choose the category, and say why. Tick one frame and write the competitive alternative it implies: what a buyer in this frame would use if Kettle did not exist. If you cannot name the alternative, the frame is a slogan.
Step 4 · Pick the size the decision needs. Go or no-go usually needs SAM; a budget or a hiring plan needs SOM; almost nothing needs TAM. Circle one and write one line on why.
Step 5 · Write the sizing question in one sentence. Category, place, year, "as a range", and the threshold it will be compared with. Read it aloud. If someone in the room would size a different thing from it, rewrite it.
Keep the page. The five lines are the top half of the one-page sizing brief in Business session 3. The bottom half, the method, the range and the assumption that would change the call, is what the analysts bring back.
Before Business session 2
30 min- Find one market size you have been shown in a deck, a board pack or a pitch. Write next to it which decision it informed, and whether that was said anywhere on the slide.
- Label it TAM, SAM or SOM, and write which of the three the decision actually needed.
- Name its category in four words or fewer, then write one other honest category for the same business and guess whether the size would go up or down.
- Bring the slide. Business session 2 reads sizing decks for the hero assumption, and yours is the first exhibit.
Three questions
Clear all three and Business session 1 gets stamped in your passport.
1 · The BD lead asks "how big is Japan for us?". What should the analyst ask before building anything?
A size is evidence for a decision. The threshold tells the analyst what the range is compared against, and when to stop measuring.
2 · For Kettle & Co, TAM is 198.24 and SAM is 19.63 billion yen a year. Why lead the go or no-go discussion with SAM?
TAM is real statistics and still the least useful: it answers how big the category is. The decision is about the part Kettle could serve.
3 · The same households and survey give 271.00 for wellness drinks and 19.63 for premium loose-leaf. Who should choose the category, and when?
The category is the output of positioning and the input to sizing. Choosing it after seeing the numbers is choosing the answer first.
What this session teaches, and where it came from
Every fact on this page, and its verification tier, is recorded in the course's source map.
Business session 1 cheat sheet · pin this
You can tie a size to a decision and choose its category on purpose. Business session 2 reads a sizing deck the way a sceptical investor would: the hero assumption that inflates a number tenfold, vanity TAMs, and analyst-report figures that arrive without a method.