Keywords · Virality · Updated 2026-07-21

What is K-factor?

Short answer: A measure of viral spread equal to the number of invitations each existing user sends multiplied by the conversion rate of those invitations.

Definition

A measure of viral spread equal to the number of invitations each existing user sends multiplied by the conversion rate of those invitations.

Why it matters for growth

A K-factor above 1 means a product can theoretically grow without any paid acquisition, since each user brings in more than one new user on average.

Example

If each user invites 5 friends and 25% convert, the K-factor is 1.25, meaning the user base compounds even with zero ad spend.

FAQ

What is K-factor?
A measure of viral spread equal to the number of invitations each existing user sends multiplied by the conversion rate of those invitations.
Why does K-factor matter for growth?
A K-factor above 1 means a product can theoretically grow without any paid acquisition, since each user brings in more than one new user on average.
What is an example of K-factor?
If each user invites 5 friends and 25% convert, the K-factor is 1.25, meaning the user base compounds even with zero ad spend.
What is K-factor? Definition and growth use · Cofounderbase