Sizing a market when there's no public data — a founder's playbook

Section 1 of 4

Why top-down sizing is useless

Top-down sizing goes: 'There are 1.4 billion people in India. 30% are middle-class. 5% of those buy what we sell. That's 20 million × ₹2000 ARPU = ₹40,000 crores TAM.'

Every number in that calculation is a guess. The percentages are made up. The ARPU is wishful. The 'middle class' is undefined. And the final number is so large it tells you nothing about whether the business is viable at your specific stage.

Section 2 of 4

Bottom-up sizing in 5 steps

Bottom-up means starting from real, countable things and aggregating up. The numbers are smaller; they're also defensible.

1. 1

   Define your unit customer precisely

   Not 'small businesses'. 'Independent dental clinics in Tier-1 Indian cities with 1-3 doctors'. Specific enough that you could list 20 of them by name.

2. 2

   Count the unit

   How many of THAT specific customer exist? Indian Dental Association registries, MCA filings, GST registrations by SIC code, local trade-association membership lists. Real lists, not assumptions.

3. 3

   Define what they currently spend on this problem

   Not 'what they would spend'. What they spend today. Phone calls to 10 of them: 'What do you spend monthly on X?' Average their answers.

4. 4

   Multiply, but conservatively

   Realistically, you can convert 0.5-2% of an addressable category in the first year. Not 10%. So: 10,000 dental clinics × ₹20k/month spend × 1% capture = ₹24L MRR in year 1.

5. 5

   Sanity-check against a comparable

   Does another business in an adjacent market do roughly that revenue? If they do ₹3 crore ARR at year 2 in a similar category, ₹24L MRR in year 1 is plausible. If they do ₹30 crore, you might be underestimating.

Section 3 of 4

Where to find real data in India and emerging markets

Public Statista / Gartner reports rarely cover regional sub-segments. The real data sources are local and unglamorous.

• MCA21 + Tofler / Zauba — every Indian Pvt Ltd / LLP filing is public. Search by SIC code, by city, by activity description.
• GST registry — turnover bands by registered business. Useful for B2B sizing.
• Udyam registry — every MSME registration in India, free to query.
• Trade association directories — IDA (Indian Dental Association), FAIIDA, FHRAI, FICCI, CII — sector-specific membership counts.
• Local Chamber of Commerce — usually free; member lists are publicly viewable.
• Job listings on Naukri / LinkedIn — proxies how many companies hire for a given role / function.
• Reviews on Google + Justdial + IndiaMART — number of listed businesses in a category in a city is a hard count.
• Census data — older but useful for demographics. Use sparingly.

Section 4 of 4

When sizing is wrong — and how you'll know

You'll know the size estimate is wrong when:

Conversion rates don't behave. If you projected 1% capture but real conversion is 0.1%, your unit count or unit-spend assumption is off. Recalibrate.

The first 10 customers cost 5x what you predicted. CAC reality vs your assumption. The market may be more fragmented than you sized for.

Competitors you'd never heard of show up. Means the market is more crowded than your bottom-up suggested. The real addressable share is smaller.

Good founders re-size every quarter for the first two years. The estimate at month 1 is your best guess; the estimate at month 24 is closer to truth.