Viral Growth

The growth mechanism a product owns when existing users recruit new ones, measured by the viral coefficient. Product Led Growth — The End User Era gives the explicit formula Kyle captured: ”(#) Invitations Sent per User x (%) Conversion Rate = (#) Viral Coefficient.” The book treats viral loops, Network Effects, and Word of Mouth as a dedicated growth surface — “the product itself then drives end user conversion and expansion through increased usage, viral loops, collaboration and word-of-mouth referrals” — with the blunt prerequisite that “the key to word of mouth is simple: Have a product that is so awesome people just can’t stop talking about it.”

In the book’s framing this is also how the Consumerization of the Enterprise plays out: viral, network-effect products like Calendly are “really just targeting consumers inside an enterprise,” so consumer-style invitation-and-conversion tactics apply inside the org. Kyle rated the book 2/5 — useful as a field guide to the PLG vocabulary (viral coefficient, PQLs, land-and-expand, North Star metrics) rather than a unifying theory — so this page inherits the taxonomy, not a thesis.

Context: “Viral growth” / “virality” is a standard growth-marketing concept: a viral coefficient (k) above 1 means each user brings in more than one new user, producing self-sustaining exponential growth; below 1, virality amplifies other acquisition channels but doesn’t sustain growth on its own.

Where this appears

• Product Led Growth — The End User Era — dedicates a section to viral growth, the viral-coefficient formula, and viral loops; ties virality to Network Effects, Word of Mouth, and consumer tactics applied inside the enterprise (Calendly)