✍️ Essay
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Free
Intermediate
Why we picked it
This is the sharpest short essay on why a naive market number lies to you. Evans shows that a new product can either shrink a market (cheaper, lower revenue per user) or explode it (many more users, new uses), so copying an existing industry's revenue is not your TAM. Read it before you write a single number, because it reframes TAM as a judgment about who buys and why, not a spreadsheet.
From
Benedict Evans
by Benedict Evans
about 1,200 words
- A better, cheaper product changes the market, so today's industry size is only a proxy
- Ask who buys now and who buys once it is good enough and affordable
- Numbers are a starting point for judgment, not a substitute for it
Open
ben-evans.com →
✍️ Essay
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Free
Intermediate
Why we picked it
When there is no category report to point at, you have to build the number yourself, and this is the essay that teaches you how. It walks through bottoms-up sizing (start from your actual customer, their willingness to pay, and how you will reach them) and shows why the top-down 'we just need 1 percent of a huge market' story falls apart. Treat it as the method for a defensible estimate, not a promise about how big you will get.
From
Andreessen Horowitz
by Anu Hariharan, Frank Chen, Jeff Jordan
~20 min read
- Build TAM from the bottom up: real customer profile times realistic price times how many you can actually reach and sell to.
- Top-down percentages inflate the number and hide the hard part, which is distribution and go to market.
- Some of the best companies (eBay, Airbnb) started against a market that looked small, then expanded the use case, so a modest starting number is not a dealbreaker.
Open
a16z.com →
✍️ Essay
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Free
Intermediate
Why we picked it
Most market sizing advice online is generic TAM SAM SOM filler. This one is written by an investor, backed by a survey of 30 VCs, and it is honest about the thing that matters: a big number pulled from an industry report proves nothing. It walks you through building the number bottom up (customers times what they pay you per year), which forces you to confront whether real people will actually pay, and that is the honest test of whether an idea can grow past a niche.
From
Pear VC
by Ian Taylor
~15 min read
- Size the market bottom up (count of real customers times annual revenue per customer), not by claiming a percent of some giant top down figure.
- TAM, SAM, and SOM are used loosely across the industry, so state your assumptions plainly instead of hiding behind the acronyms.
- Project the market out five or more years and include how you would actually reach and acquire customers, since a market you cannot serve is not your market.
Open
pear.vc →
✍️ Essay
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Free
Advanced
Why we picked it
Before you sweat which side to seed, Gurley helps you judge whether your marketplace is even structurally worth building. He lays out ten factors (fragmentation, frequency, payment flow, network effects) that separate marketplaces that snowball from ones that stay empty. It is the investor lens on why some two sided ideas never reach liquidity no matter how hard you push.
From
Above the Crowd
by Bill Gurley
20 min read
- Great marketplaces enhance a market, they do not just aggregate it
- High fragmentation on both sides makes a marketplace more defensible
- Being in the payment flow is far stronger than sitting outside it
Open
abovethecrowd.com →
📖 Book
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Paid
Beginner
Why we picked it
The single best thing ever written on customer conversations. It teaches you to ask about the customer's life and past behaviour, not your idea, so you can't be lied to. If a founder reads one thing before talking to a single customer, it's this.
From
momtestbook.com
by Rob Fitzpatrick
~130 pages
- Talk about their life, not your idea.
- Ask about specifics in the past, not opinions about the future.
- 'That's so cool, I'd totally buy it' is a compliment, not data, dig for commitment and evidence.
Open
momtestbook.com →
📄 Article
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Freemium
Intermediate
Why we picked it
Kamps has seen more market-size slides than almost anyone and calls out the exact failures founders repeat, including claiming a whole industry as your TAM. It is a fast reality check on what makes an investor stop trusting your numbers. Read it to catch the mistakes in your own deck before someone else does.
From
TechCrunch
by Haje Jan Kamps
- Claiming an entire industry as your TAM signals lazy thinking
- Your TAM is what you can earn, not what your customers earn
- A defensible smaller number beats an indefensible huge one
Open
techcrunch.com →
📄 Article
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Freemium
Intermediate
Why we picked it
This is a real deck with the market slide critiqued line by line, showing how a founder listed the entire sharing economy at hundreds of billions when the honest number was the rental equipment market worth a few billion. Seeing the correction on a real example makes the top-down trap concrete in a way definitions cannot. Use it as a model for how narrow and specific your own slide should be.
From
TechCrunch
by Haje Jan Kamps
- A real deck shows the gap between claimed TAM and defensible TAM
- Size the market you actually serve, not the adjacent giant one
- Specific and smaller reads as more credible to investors
Open
techcrunch.com →
📄 Article
✓ Link checked
Free
Beginner
Why we picked it
This lays out both the top-down (start from a big industry number) and bottom-up (build up from your own price times likely customers) ways to size a market, with formulas and a worked example. The bottom-up method is the one you can actually run over a weekend with public numbers and honest assumptions, no paid report needed. Use it to reach a rough first estimate you can defend, then keep refining as you learn.
From
HubSpot Blog
by Clifford Chi
~12 min read
- Bottom-up sizing (customers you can realistically reach times your price) is more defensible for an early founder than a scary top-down billion-dollar number.
- Free public inputs get you far: company 10-K filings, government statistics, and competitor customer counts stand in for paid reports.
- Run both top-down and bottom-up and see if they roughly agree; a wide gap means one of your assumptions is off.
Open
blog.hubspot.com →
📄 Article
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Free
Beginner
Why we picked it
Written from an early-stage investor's chair, this walks the calculation with examples and is blunt that a bottom-up build beats a share-of-TAM guess. Antler backs pre-seed founders, so the advice is calibrated to exactly the stage you are at. Useful for seeing how a fund wants the number presented.
From
Antler
by Akshat Agarwal
- Early-stage investors prefer a bottom-up build over a share of TAM
- Worked examples show each of the three numbers being derived
- Present the assumptions so the number can be stress-tested
Open
antler.co →
📄 Article
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Free
Intermediate
Why we picked it
This one focuses squarely on the method your short answer champions, building TAM up from real customer counts and pricing rather than slicing a giant number down. It is a good deep dive once you accept that bottom-up is the way and want the mechanics. Practical on ICP counts, adoption assumptions, and unit economics.
From
Qubit Capital
by Qubit Capital
- Build from your ideal customer profile count times annual value
- Ground adoption rates and pricing in observable segments
- Bottom-up assumptions can be tested, top-down percentages cannot
Open
qubit.capital →
📄 Article
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India
Free
Intermediate
Why we picked it
Blume's annual report is the single best data-grounded read on what is actually happening in Indian internet and consumption, not what is trending on VC Twitter in San Francisco. It shows you adoption curves (UPI, quick commerce, ONDC, how few households actually shop online) so you can pressure-test whether a hyped trend has the demand base to land here. Treat it as a starting map of Indian reality, then judge your specific trend against it.
From
Blume Ventures
by Sajith Pai, Anurag Pagaria and team (Blume Ventures)
~180 charts
- Grounds trend-spotting in real Indian adoption data (income distribution, online-shopping penetration, UPI-native monetization) instead of imported hype.
- Indian startups are building a distinct playbook (micro-subscriptions on UPI Autopay, DPI rails) that has no clean US analogue, so copying a US trend directly often misses the real opportunity.
- A trend can be huge in raw numbers yet thin in monetizable demand: the report repeatedly separates users from paying users.
Open
blume.vc →
📄 Article
Free
Intermediate
Why we picked it
A clear, no-nonsense primer on the three market-size numbers every founder gets asked about, with the bottom-up method that actually holds up in front of investors. Pick this over the SEO listicles because it comes from a platform that lives inside real cap tables and fundraises.
From
carta.com
by Carta
~12 min read
- TAM is the whole category, SAM is what you can realistically serve, SOM is what you can win near-term.
- Build the numbers bottom-up (customers times price), not top-down percentages of a giant number.
- A defensible SOM matters more to investors than an impressive TAM slide.
Open
carta.com →
