Product market fit is one of the most talked about but least understood aspects of early stage startup growth. It’s a favorite subject among angel investors and founders alike and or good reason – it often points to the first major inflection point of a startup – the potential to scale.

In my experience working with now hundreds of startups, I’ve often been surprised at how little this concept is understood. So I set out to try to define what product market fit is, as well as outline a couple resources for measuring whether or not you have it.

In researching a definition, I came across this Wikipedia article which says that there are 2 popular ways to measure PM fit:

1. The 40% rule

According to Wikipedia, you have PM fit if “at least 40% percent of surveyed customers indicate that they would be ‘very disappointed’ if they no longer have access to a particular product or service. Alternatively, it could be measured by having at...