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The Only Leading Metric to Measure Product-Market Fit and How to Use It

Product-market fit (PMF) is a tricky thing for startups. It’s that sweet spot where the needs of your target market perfectly align with what your product is offering, and if you’re a product manager at an early startup, it’s your job to help your product find that fit.

A lot of startups think they have PMF and try to enter the growth phase prematurely — usually due in part due to VC pressure to grow or simply not having a way to measure and validate how strong your PMF is — which can be disastrous.

Since PMF usually shows up as more of a gradient rather than a binary quality (you might have a somewhat of a weak PMF or a very strong PMF) it can be difficult to truly say with confidence that you’ve found it.

On top of that, no one seems to have a quantitative definition for how to measure it. Until the 40% rule.

Leading indicators > lagging indicators

Sean Ellis is credited with popularizing the 40% rule. It states that if 40% or more of your users would be “very disappointed” if they could no longer use your product, then you’ve achieved product-market fit.

I’ve helped a lot of products and companies build a product from 0 to 1, but very few people bring up the 40% rule as a goal for the new product.

Even when I search for “how to find product market fit,” I find vague articles describing how you should understand your target persona, test prototypes, etc., but nothing around how to measure it.

Marc Andreessen describes PMF in his 2007 blog post:

“You can always feel when product/market fit is not happening. The customers aren’t quite getting value out of the product, word of mouth isn’t spreading, usage isn’t growing that fast, press reviews are kind of ‘blah,’ the sales cycle takes too long, and lots of deals never close.”

“And you can always feel product/market fit when it is happening. The customers are buying the product just as fast as you can make it — or usage is growing just as fast as you can add more servers. Money from customers is piling up in your company checking account. You’re hiring sales and customer support staff as fast as you can. Reporters are calling because they’ve heard about your hot new thing and they want to talk to you about it. You start getting entrepreneur of the year awards from Harvard Business School. Investment bankers are staking out your house.”

Illustrative, but vague.

What Marc mentions above are all lagging indicators of PMF. But what if you had a leading indicator of PMF? Is this something you can even measure? If you can measure it, can you systematically increase it?

One PMF survey to rule them all

If you simply want to measure whether you have PMF, you can do that by sending out a simple survey to your existing users to see how many of them would be “very disappointed” if they could no longer use your product.

If more than 40% of your users categorize themselves as being super disappointed if they lost access to your product, you’ve more than likely achieved PMF.

Most articles I’ve read on this topic just stop there. They just count how many people would be very disappointed. But if you read some of Rahul Vohra’s articles — the person who took the 40% rule and turned it into a survey — he goes further and utilizes the survey to actually help inform what features to put on his product roadmap in a very systematic way.

This was such a key insight for me, personally, because it’s not like you get PMF and you’re done. You need to keep earning it and making it stronger. There are obviously no silver bullets in building a successful product, but it’s important to build repeatable systems to replicate success in a structured way.

The survey consists of four questions and each question is essentially a kind of filtering mechanism to ultimately figure out which customer segment’s feedback you should prioritize when thinking about how to improve your product’s PMF.

  1. How would you feel if you could no longer use [product]?
    • Very disappointed
    • Somewhat disappointed
    • Not disappointed at all
    • I no longer use this product
  2. What type of people would benefit from [product]?
  3. What’s the main benefit you receive from [product]?
  4. How can we improve [product]?

How to fully leverage the survey

Q1: How would you feel if you could no longer use [product]?

By asking your customers to rate their level of disappointment in the first question, you’re able to segment your customer base and decide which customers to focus on.

If we assume that your product is delivering on your core value proposition and a customer isn’t at all disappointed about not being able to use your product, then they probably aren’t your target demographic.

The user’s answer to this question will determine which feedback you should prioritize in questions 3 and 4.

Q2: What type of people would benefit from [product]?

The second question is pure gold because your users are describing themselves in their own words, helping you further understand how to get more users in your target persona.

Understanding your own customers through the lens in which they see themselves can be a super powerful tool. As Rahul says, “They’re essentially writing your marketing copy and your landing page for you.”

Q3: What’s the main benefit you receive from [product]?

In the third question, your users tell you why they love your product. Rahul recommends throwing all the responses in a word cloud to see what the primary reasons your users love your product.

Most of your time may be focused on improving your product, but equally important is understanding what your product already does well so that you can preserve that.

Put questions 3 and 4 in separate word clouds so you can easily see the main benefit they receive from your product and how they want to see the product improve. This is just a random image of a word cloud, hopefully your product feedback is more useful than this. Photo from mentimeter.

Q4: How can we improve [product]?

In the fourth question, in Rahul’s words, you’re essentially asking users what’s holding them back from loving your product even more. He also recommends putting the responses to this question in a word cloud to easily visualize the most common suggestions. This question is where you’re sourcing feedback about what to build next on your roadmap.

But should you listen to feedback from all your users?


We should prioritize feedback from users who resonate with the primary value proposition of your product.

Let’s use Rahul’s product, Superhuman, as an example. Superhuman is essentially a premium email product whose primary value proposition is speed. In question 3, we’re looking for users who answered that the main benefit they receive from the product is aligned with the core value proposition — speed.

So before putting all the short form answers in a word cloud and treating all feedback equally, segment your users based on how they answered question 1 and question 3 to find and prioritize your target user persona.

Here’s a matrix of which user segment’s feedback you should prioritize based on people’s responses to question 1 and 3. You’ll want to prioritize the people who said that the main benefit they receive is aligned with the core value prop of your product AND who either responded that they would be very disappointed or somewhat disappointed if they could no longer use your product.

If we assume your product is delivering on your core value proposition but a user cites the main value they receive from the product is something other than your core value prop, regardless of their answer to how they would feel if they could no longer use the product, their feedback in question 4 when you ask, “how can we improve [product]?” is not the first priority.

In order for us to build a cohesive product experience, we need to stay laser focused on our target persona. If we are building a product who’s primary value prop is speed of receiving/sending emails, what would happen to the product if we started building all the features that other non-target personas wanted? The product wouldn’t fail necessarily, but the focus of the product would get diluted over time and weaken PMF.

If a customer does identify that the main benefit they receive from your product is that it aligns with the core value prop but they “wouldn’t be disappointed at all” if you took the product away (okay, ouch), they might be your target customer but they’re also probably going to be very difficult/costly to convert into one of your 1,000 true fans.

Now, a caveat here, it’s not that you would ignore this feedback completely, but you need to prioritize and understand the most important customer segments to listen to when asking “how can we improve [product]?”. Different customers have different levels of product-customer fit.

The people who would be “very disappointed” if they could no longer use your product are already sold on your product. Great! They’re the individuals who have the strongest product-customer fit. You want to pay attention to their feedback in question 4, but they are not the top priority. They’re already in love with your product. Regardless of what new feature you add, they are mostly going to still give you a high score of “I’ll be very disappointed if I lose this product.”

If they are not your top priority, then who is?

The people who would be “somewhat disappointed” if they couldn’t use your product anymore and whose main benefit was aligned to the core value proposition! This is where you need to focus your attention. They’re on the fence about loving your product, the core value prop resonates with them and something small is just holding them back. Listen to what’s missing for these folks, deliver on it, and watch your PMF score soar.

Putting it all together

As you can see, finding product-market fit is inextricably tied with finding product-customer fit. The better you understand who your target customer is, the more focused and disciplined you can be about who’s feedback to listen to and how. This method gives you extremely tactical steps on how to do that.

By prioritizing feedback from users who resonate with the core value proposition and who are on the fence about falling in love with your product, this system provides a jumping off point for you to hone in on what product outcomes to produce first.

As product managers, we need to create feedback loops for ourselves, but we also need a system about which feedback to prioritize and which feedback to politely put to the side. In that way, this framework is also useful for products who’ve already found PMF.