Testing Product-Market fit of an existing Product

Measuring Product-Market Fit in a quantifiable way, using the Product Market fit formula: " How would you feel if you could no longer use this product?:

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Also see: How to Monitor Customer Satisfaction & Loyalty (NPS)

Testing Product-Market fit of an Product idea

Using just a short description of the problem you're trying to solve and the solution you're proposing proved.co  can benchmark your idea. They use a large panel to answer a few questions about your concept. 

Further reading

Great article/case study on measuring and improving product market fit: https://firstround.com/review/how-superhuman-built-an-engine-to-find-product-market-fit/