All termsGROWTH & ACQUISITION

Viral Coefficient

Also known as: K-factor

DEFINITION

The average number of new users each existing user brings in — the mechanism behind compound product-led growth.

In depth

K-factor = (invites sent per user) × (conversion rate of invites). K > 1 means every user brings more than one new user, and growth compounds without advertising. K = 0.5 means for every 100 users you acquire, organic growth adds another 50 automatically.

True K > 1 is rare outside consumer social. For SaaS, focus on K between 0.3–0.7 as a strong supplement to paid acquisition.

Formula & example

K = invites sent per user × conversion rate of invites

Related terms

PLG

A go-to-market motion where the product itself is the primary driver of acquisition, activation, and expansion — rather than sales.

Network Effects

A product property where each additional user makes the product more valuable to existing users.

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Last reviewed 14 April 2026 by Abhi Verma.