Sizing a market you haven't entered yet

The Founders work group compares how Notion, Pinterest, Coda, Twitch and LinkedIn judged their markets and where their numbers came from.

Updated October 13, 2026

Start from a behavior people already have, ask why nobody has won the market yet, and let growth or repeat use tell you how big it is.

Set a ceiling with a ratio. Ivan Zhao never built a bottoms-up TAM for Notion. He used the gap between 1B+ knowledge workers and about 25M developers, and notes as a daily habit for 1B+ people. He would find a behavior with a long history and put the idea inside a familiar form. After Ben's pushback, he counts that history as the part of the test that carries weight, with a paid predecessor as a stronger signal for a business product.
Research the behavior first. Ben Silbermann thinks a sizing exercise in 2009 would probably have talked Pinterest out of it. Collecting was the real opportunity. He would watch whether an unexpected use, like Pinterest's boards of inspirational quotes, holds up as the product grows past early adopters.
Ask why nobody has won it. Shishir Mehrotra writes down the assumption the market has made that his team sees differently, then asks whether it's true and what has kept anyone from acting on it. For Coda, file formats had been the lock-in, and web tools removed it. An idea Microsoft could ship in a release is not a company, in his view.
Let growth stand in for size. Emmett Shear funded Justin.tv's gaming and mobile side projects with growth goals set in advance. Gaming grew 25 to 30% a month for almost nine months before Twitch launched. In a two-sided market, he would research first the side the other side is loyal to.
Write down what would prove there's no market. Reid Hoffman would write the thesis before building: what you believe that others don't, what would show there is no market, and how you will get fast adoption anyway. Hardware needs harder evidence before you commit capital than software does.

Group chat with Emmett, Ben, Ivan, Reid, Shishir — the Founders work group

Question:

How do you research and size a market before you build?

Ivan ZhaoFounder of Notion

So, I never built a bottoms-up TAM spreadsheet for Notion. I sized it with two ratios and one historical question.

The first ratio came from our 2021 funding post. The world runs on software used by 1B+ knowledge workers, but only about 25M developers can modify it. Our whole product mission is closing that gap, so the gap told us how big the market could be.

The second number was the entry use case. Notes and docs are something 1B+ people do every day. We picked that wedge because it gave us the biggest possible top of funnel, and our internal strategy, "B2C2B," depended on it. Individuals use Notion for simple note taking, find the relational database underneath, and then bring it to work. Half our B2B customers came in that way.

Apple Podcasts

The historical question was whether the market is bundling or unbundling right now. Microsoft bundled software in the 90s, and SaaS unbundled it until the average company was running close to 100 tools. Reading where you are in that cycle tells you whether to build vertical or horizontal, and those two choices produce very different businesses.

Apple Podcasts

Now the honest trade-off. A vertical company gets a market boundary for free: you sell to one or two personas, and it's clear who buys. A horizontal company has no boundary, because Notion goes after the entire software market, so you have to draw that boundary yourself through positioning and go-to-market. I stayed in the "Lego brick" mindset for too long. I wish we had started selling the "solution Lego box" to businesses and moved upmarket earlier.

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I also wouldn't recommend the horizontal path to most founders. The problem space is too large for a playbook to exist, and horizontal products usually take years to find fit. Ours did too.

Ben SilbermannFounder and Chairman of Pinterest. Founder of How We Feel

Ivan had a number to start from, 1B+ people taking notes. Pinterest didn't have a clean one, and a market-sizing exercise in 2009 would probably have talked us out of it. Pinterest went against what was popular in Silicon Valley at the time. Facebook, Twitter and FriendFeed were real-time text streams, and we were images that weren't real-time. Many VCs passed on us for that reason.

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So I'd research a human behavior before I'd research a market. I've been a collector since I was a kid: stamps, baseball cards, and insects I caught growing up in Iowa. I think most people collect something in some part of their life, and that habit was the real size of the opportunity.

YouTube

The research that mattered came after we shipped. When we launched, I emailed all my friends and nobody really got it. A small group did love it, and they weren't typical early adopters. They were people I grew up with, using it to plan their homes and pick recipes. So we asked where those people gathered. The answer was a blogger conference, and we had each blogger introduce Pinterest to their own readers.

YouTube Three months after launch we had about 3,000 accounts, and we built around that small group of fanatical users.

forbes

One more step comes before any of this. Ship once you have one thing you're proud of. Our first attempt, an iPhone shopping app called Tote, crammed in too many features and wasn't great at any of them. If a product isn't worth someone's time, the feedback you get only tells you what you already knew.

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The limit of my approach is that it was slow. It worked for a consumer product with almost no capital needs. If your build costs a lot up front, you'll need a harder number earlier.

Shishir MehrotraCEO of Superhuman (formerly Grammarly). Co-founder of Coda and former Chief Product Officer of YouTube

Ivan's ratios tell you how big the prize could be. Before I trusted a number like that, I wanted to know why nobody had won it yet. So I start by writing down one simple insight: the assumption everyone else in the market has made that we see differently. Then I put that insight through two tests. First, is it actually true? Second, what has kept anyone from acting on it already?

Apple Podcasts

At Coda, the insight was that companies draw an artificial line between docs and apps. The sizing came from that line. The average company buys something like 265 different software applications, and a large share of them exist because a doc couldn't do the job.

Spotify

The second test, about the barrier, is where I spent most of my research time. I went back through the history of documents and found that Apple was arguably the best innovator of the late 1990s and early 2000s. Numbers, Pages and Keynote were all different from Word, Excel and PowerPoint, and none of them took off. File formats were the reason. If you sent someone a Keynote file, they needed a Mac to open it, so format compatibility became real lock-in. Even Google Docs had to import and export Office files with full fidelity. Web-based tools removed that barrier, and that change is what made the timing work for us.

The feature-or-product question filters out a lot of ideas. When I described Coda, people kept suggesting things like "Office with different line spacing." If Microsoft could ship an idea in a release, it's probably only a matter of time before they do, and you can't build a company on it.

Once something is live, I watch two signals. I ask users what Coda replaced, and the answers varied a lot, which told us the market was a bundle of smaller ones. That fits Ivan's bundling cycle from the customer's side.

Spotify Early on I also trust Rahul Vohra's disappointment score more than NPS, because a differentiated product in a young market shows up there first.

Emmett ShearCEO of Softmax. Founder of Justin.tv and former CEO of Twitch

Ivan's ratios work for setting a ceiling on a horizontal product. They don't tell you whether anyone wants your version yet. By the time a TAM figure feels convincing, someone else has usually seen it too, so what I measure is whether a real slice of the market is already pulling on you, and then I study that slice's customers until I understand what they actually want.

Twitch is the clearest example. Justin.tv gaming had been growing 25 to 30% a month for almost nine months before we launched Twitch as its own site, so it was fully validated before we bought the new domain

Apple Podcasts. We set that bet up deliberately. Instead of arguing about which pivot was bigger, we funded gaming and mobile as small side projects with growth goals, and agreed to pivot to whichever one hit them

Apple Podcasts. In that setup, observed growth stands in for market size.

The research itself was interviews with streamers. I asked what tools they used, what they liked, and what they wished someone would build for them. Their feature ideas didn't matter much. The follow-up did: "I built you the big red button. Why is your life better now?" That question gets you to the real need

Spotify. The first round boiled down to three things streamers wanted: money, fame, and love. Once we met those needs and had a way to acquire streamers, growth took off almost immediately

Spotify.

I also held off on forming hypotheses during those interviews. Once you have a theory, you start hunting for evidence that confirms or disconfirms it, and you miss the bigger picture

Spotify.

The failure case is Kiko. We built a calendar app even though we didn't really use calendars beyond the one in Gmail. So when Google launched its own calendar, we had no idea what to do next

Apple Podcasts. If you aren't the customer, you have to go talk to the customer before you build.

Ben SilbermannFounder and Chairman of Pinterest. Founder of How We Feel

Shishir's "what did it replace" question has a cousin I'd add to the list: what are people using it for that you didn't design for? On early Pinterest, a lot of people made boards of things that made them happy or relaxed them, mostly inspirational quotes. We didn't know what to make of it and assumed it was a quirk of a small early user base. It held up all the way to a quarter billion users, and it's still one of the most common ways people use Pinterest.

YouTube

That pattern told me something no market report would have. People want tools that help them feel good about themselves, and they'll put in the work to build those spaces. Technology companies rarely talk about emotions, so no category existed to size it against. So the evidence was the behavior itself, repeated at scale by people we'd never met.

So my sizing test is about persistence. When an unexpected use shows up in your first few thousand users, watch whether it survives as you grow into people who aren't like your early adopters. If it does, you've found a need that's larger than the product you thought you were building.

Ivan ZhaoFounder of Notion

Emmett is right that my ratios say nothing about whether anyone wants your version, and Notion paid for learning that. I agree with Ben that the behavior is the real research. Notion's first version took our mission literally: everybody should be able to create software, so we built a developer tool simple enough for anyone. We spent a couple of years on it, gave it to friends and investors, and it didn't resonate. Most people wake up with a report due. They want to get the job done, and they don't care about building software to optimize it.

Apple Podcasts

So we hid the vision inside a form people already used every day, which was productivity software. That changed how I think about market research. When people asked how we knew Notion was wanted, my answer was that its previous versions had existed for decades. Word and Office. Lotus 1-2-3 in the 80s. Before that, typewriters and file cabinets.

Spotify If people have done something for 50 years on paper and then on three generations of software, the demand is already proven. Your research question becomes narrower: what does the current version get wrong?

Ben's point about fit holds for this approach too. Finding the right market didn't save us on its own. We had the right shape, productivity software with the building blocks underneath, but we were on the wrong technical foundation and running out of money. We laid off all five people, leaving Simon and me, and rebuilt it in Kyoto.

YouTube

My concrete method is to find a behavior with a long history, check that people already pay for an older tool that serves it, and then put your more ambitious idea inside that familiar form.

Reid HoffmanCo-founder of LinkedIn, Inflection AI and Manas AI. Partner at Greylock

Emmett's warning about forming hypotheses too early is right for customer interviews, but I'd still write the market thesis down before building. When a market doesn't exist yet, it usually ends up either huge or non-existent. A thesis written in advance is how you tell which one you're facing before you've spent two years finding out

YouTube.

The thesis has two halves. Shishir covered the first, the thing you believe that others don't. For LinkedIn, mine was that recruiting through classified ads belonged to the newspaper era. In a networked age, you recruit people directly through their professional networks. That one was relatively easy to validate

YouTube.

The second half gets skipped more often. Write down what would lead you to conclude there's no market. Then put the thesis up against the classic entrepreneurial misfire, the assumption that once the product exists, people will realize they love it and line up in droves. A few founders, Steve Jobs among them, could make that happen. Most of the time it doesn't work, because people adopt slowly when they don't know they want the category. So your thesis has to explain how you'll get fast adoption anyway

YouTube.

Ben's story with the bloggers and Emmett's 25 to 30% monthly growth on Justin.tv gaming are both examples of that adoption path, observed in practice. Each one gives you a concrete signal you can name in advance. You keep the thesis and the listening separate: you commit up front to what would prove you wrong, and you go into the interviews open.

How much you validate before building depends on the domain. In software, speed of learning matters most, so you ship early and let usage do the research

Spotify. In hardware, shipping the wrong thing can kill you, so the thesis needs much harder evidence before you commit capital

YouTube.

Shishir MehrotraCEO of Superhuman (formerly Grammarly). Co-founder of Coda and former Chief Product Officer of YouTube

I partly disagree with Emmett on studying the slice that's already pulling on you. That works when the slice is using the whole product. At Coda, our first real users were a single team led by Noam. One day they stopped using it, all of them, which was 100% of our user base. They handed us a list of about 30 things to fix and said they'd come back when we were ready. Every idea on the list was good, and it felt like someone had given us a roadmap. We chose not to build it. Coda was mostly tables then, with no document, forms or layouts yet, so Noam's team only saw a small part of what we were building. If we had overfit to that list, we would have missed what the product was meant to become. It took us two to three years to get through their list, and we did it while building everything else.

Apple Podcasts

So for an all-in-one product, the early customer signal tells you about the piece they can see. It won't tell you how big the whole market is. That's why we defined product-market fit as spread. For a team product, fit means someone on one team carries Coda into a different team. We didn't see that until our first beta, about three and a half years in.

Disappointment score and NPS can also disagree, which says something about the market itself. Coda had high disappointment scores and low NPS early on, and Superhuman had the reverse. Superhuman users loved it and recommended it, but Gmail was right there if it went away. Coda users had no substitute, though they weren't yet confident recommending it. When disappointment is high and NPS is low, you've found a gap nobody else fills. High NPS with low disappointment means you're competing in a market that already has alternatives.

Emmett's Kiko story passes the same test I described earlier. A calendar was something Google could ship as a feature, and it did.

Emmett ShearCEO of Softmax. Founder of Justin.tv and former CEO of Twitch

Ben's unexpected-use test is how Justin.tv found its real market. We started out producing a live reality show about Justin's life, and we were bad at it. That turned out not to matter. As a customer, we weren't that different from everyone else who wanted to broadcast live, and lots of people wanted to stream live on the internet

Spotify. The show was the product we designed. The thing people actually used was the streaming tool underneath it.

The second lesson took longer. In a two-sided market, you have to work out which side the market really is. When I started watching gaming streams, I saw that my loyalty was to the streamer and not to Justin.tv. If my favorite streamer moved to YouTube, I would have followed them. I also didn't want to be a streamer, so my own intuition as a user was pointing at the wrong customer

Spotify.

That changes how you count. Viewers look like the big number, but streamers decide where viewers go. Every streamer we recruited brought their audience with them by telling followers to come watch on Twitch. We paid some of the larger streamers $1,000 to switch, and we used their complaints as our feature request list. Shishir, this is where I'd answer your Noam story. We often didn't build the thing a streamer suggested. We went and solved the problem they were pointing at

Apple Podcasts. Studying the slice that's pulling on you means learning what they need, and their roadmap is only evidence of it. So the market worth researching was a few thousand gaming streamers and what they needed, and the viewer numbers followed from that.

If you're sizing a marketplace or a creator platform, start by finding the side that the other side is loyal to. Research that side first.

Reid, I agree with keeping the written thesis separate from the listening. Our side-project setup was exactly that: we wrote the growth goals for gaming and mobile down in advance, and missing them would have killed the project

Apple Podcasts. The goals were the kill criterion. I kept theories out of the streamer interviews themselves, because those were where the money, fame, and love answer came from.

Ben SilbermannFounder and Chairman of Pinterest. Founder of How We Feel

Ivan's test of checking that people already pay for an older tool works well for productivity software. It breaks down for some of the needs I've cared most about, because people meet them without paying anyone. Collecting is a good example. For most of history it lived in shoeboxes, binders, and cases of beetles on a bedroom shelf, and you couldn't put a revenue line on any of them.

YouTube

So when there's no paid predecessor, I look for experts who have studied the behavior for years and build with them. How We Feel started in 2020 as a nonprofit app I built with scientists at MIT and the Harvard School of Public Health. You entered your ZIP code and how you were feeling, and the researchers used that data.

Spotify We went to the scientists first because they already knew which questions mattered and what was still unknown.

In that same conversation, I agreed with Jeff Lawson's view that you work backwards from what people are experiencing and the problems they need to solve, and everything else follows.

Spotify For a free or nonprofit product, the "market" you're sizing is a count of people with a real need. You measure it in how often they come back, because they'll never show up as dollars.

Ivan ZhaoFounder of Notion

Ben, fair correction. The part of my test that carries weight is the long history of the behavior. A paid predecessor makes the signal stronger for a business product, and How We Feel shows you can do without one. Reid's question of how adoption actually happens was half of our mission statement from early on. In our 2021 funding post I described Notion's mission as two parts: software toolmaking and ubiquity. Missing either half meant missing the whole. A tool for building software only becomes useful once lots of people around you already use it, so we planned for adoption as deliberately as for the product.

Concretely, we gave $1,000 Notion credits to startup incubators to get the startup community using it. Later we made Notion completely free for students and educators. Companies are the ones who pay, so charging students who can barely cover tuition made no sense. Our goal was for Notion to show up everywhere, the way everyone uses Microsoft Office for something.

YouTube

So my answer to Reid's test looks like this. Write down where the paying customer is (businesses). Then write down who reaches that customer first for free (individuals, students, early-stage startups). Then check whether the free use case is something people do every day, like taking notes. If it is, individuals will bring the tool to work themselves, which is the B2C2B path I mentioned earlier. B2C2B is Shishir's spread test one level down: one person carries the tool into their team. If the free use case is occasional, you won't get the fast adoption Reid is asking about, and you'll have to sell top down from day one.

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Frequently Asked Questions

What are the signs of product-market fit?
A small group who would be upset to lose the product, then growth you can explain, from users who look like the market you want to win. Fit rarely arrives as one moment.
How is early traction different from product-market fit?
Traction responds to a launch, press or founder effort and fades when that stops. Fit keeps compounding through the product's own loop, and the love repeats with strangers who match the first fans.
What should you do when product-market fit isn't coming?
Make the next attempt a bounded test with a target and a deadline the cash can cover, check that the test was fair, and change course on a miss. With no promising group or runway left, return the capital.
How do you pressure-test a startup idea?
Set a behavior bar before the team gets attached, put an early version into someone's real work, and write down the ways the company could fail even if early users love it.
When should a founder drop an idea?
When people who have the problem can find the product, try the full version and still don't come back. Low signups and investor doubt alone are weak reasons to quit.
How do founders find a problem worth solving?
Start from a problem you will care about for years, find people whose behavior shows they have it too, and know why you can make progress where others see risk.
What should a first-time founder do first?
Start, choose a cofounder with care and get something in front of strangers early. The group splits on whether research or a rough product comes first.
How does a startup stand out in a crowded market?
Pick one experience people return to, start with the people whose choice brings everyone else, and check whether users come back for a second job.
Where can an AI startup win against the model companies?
Around what takes sustained work to copy: a group's accumulated taste, a team's workflow, trust between people or a creator's audience.
How do you validate an idea with customers?
Go out to learn, ship one thing worth a stranger's time, watch who comes back on their own and then ask them why.
How do you choose a consumer products category?
Look for a need people already recognize, evidence that they act on it, and unit economics that work across the whole purchase cycle.

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Frequently Asked Questions

Sizing a market you haven't entered yet

Founders

Frequently Asked Questions

What are the signs of product-market fit?

How is early traction different from product-market fit?

What should you do when product-market fit isn't coming?

How do you pressure-test a startup idea?

When should a founder drop an idea?

How do founders find a problem worth solving?

What should a first-time founder do first?

How does a startup stand out in a crowded market?

Where can an AI startup win against the model companies?

How do you validate an idea with customers?

How do you choose a consumer products category?

Your ideas, super powered.

Sizing a market you haven't entered yet

Founders

Frequently Asked Questions

What are the signs of product-market fit?

How is early traction different from product-market fit?

What should you do when product-market fit isn't coming?

How do you pressure-test a startup idea?

When should a founder drop an idea?

How do founders find a problem worth solving?

What should a first-time founder do first?

How does a startup stand out in a crowded market?

Where can an AI startup win against the model companies?

How do you validate an idea with customers?

How do you choose a consumer products category?

Your ideas, super powered.