The­re are no strict rules for that as the who­le PMF concept is somew­hat abstract and vague. But the­re are (semi)objective ways to assess it. What exact­ly works is depen­ding on the con­text so you need to iden­ti­fy the rele­vant cri­te­ria for your case.  Howe­ver at the end it boils down to this (by Eric Ries)

If you have to ask if you have found it, you haven’t.”

Some things to monitor/measure that are indica­tors of PMF (more preci­se­ly, the “cus­to­mer love” or “mar­ket pull” part of PMF):

  • A wide­ly used mea­su­re is pro­vi­ded by Sean Ellis, who coi­ned the term Growth Hac­king. He sta­tes you’­ve reac­hed Pro­duct/­Mar­ket-Fit when at least 40% of the res­pon­dents answer the ques­tion “How disap­poin­ted would you be if this pro­duct no lon­ger exis­ted tomor­row?” with “Very Disap­poin­ted”.
  • Is Word of Mouth hap­pe­ning? Are your cus­to­mers tel­ling about you to 3rd par­ties, with no invol­ve­ment from you, which results in win­ning new busi­ness?
  • Do you get inbound leads that you can not track back to your own acti­vi­ty?
  • Are cus­to­mers trying to buy befo­re you even tried to sell?
  • Are your sales cycles get­ting shor­ter?
  • Do cus­to­mer requests gene­ra­te so much workload that you have no time to pur­sue your own deve­lop­ment ideas?

Our own for­mu­la­tion of a lit­mus test to deter­mi­ne whet­her the­re might be PMF:

Pro­vi­de evi­dence of 3 sepa­ra­te mea­su­red tests of your cus­to­mer beha­viour that demon­stra­te your product/service is sig­ni­ficant­ly (=order of mag­ni­tu­de) bet­ter than the exis­ting solu­tion.

Pro­duct Mar­ket Fit is when cus­to­mers sell for you”.

Glim­mers of fal­se hope is not the same as cus­to­mers wan­ting to rip it out of your hands. Pro­duct Mar­ket fit feels like a land­mi­ne going off.” Peter Rein­hardt

The num­ber one problem I’ve seen for star­tups, is they don’t actual­ly have product/market fit when they think they do.”Alex Schultz

80% of SaaS com­pa­nies never make pro­duct mar­ket fit.” Peter Rein­hardt

Star­tups need 2–3 times lon­ger to vali­da­te their mar­ket than most foun­ders expect. This unde­res­ti­ma­tion crea­tes the pres­su­re to sca­le pre­ma­tu­re­ly.” (Star­tup Geno­me Stu­dy)

You are able to articu­la­te your dif­fe­rent problem/solution fit(s) in detail”.

Befo­re you can achie­ve product/market fit, you need to unders­tand and be able to articu­la­te your problem/solution fit(s) in detail - not in “gene­ric” level or in gene­ric terms (https://gorillacapital.fi/problem-solution-fit/).