Product Management: Foundations to Practice · Product-Market Fit
Measuring PMF: The Sean Ellis Test
Andreessen's definition is famously hard to measure directly. Sean Ellis built the closest thing the industry has to a quantitative proxy, and this chapter covers both its power and its real limitations.
Growth expert Sean Ellis developed a measurable benchmark for product-market fit around 2010: survey active users with the question, how would you feel if you could no longer use this product, with response options of very disappointed, somewhat disappointed, and not disappointed [11]. If 40 percent or more of respondents answer very disappointed, the product is generally considered to have reached product-market fit; below that threshold signals more work is needed before scaling acquisition spend.
- The Sean Ellis test asks active users how disappointed they would be without the product; 40%+ 'very disappointed' suggests PMF.
- The 40 percent threshold was derived empirically from patterns across many startups, not a fixed mathematical law.
- The survey can produce false positives when customers respond to a product's promise rather than its delivered value.
- Flattening retention curves provide a harder-to-fake complementary signal, and segmenting results by user type adds precision.