UUID Collision Probability Calculator

Estimate collision probability for a chosen UUIDv4 count or invert a target probability using the standard birthday approximation.

Generated UUIDv4 count

Target collision probability

—Probability at count

—Percent

—Count for target p

122UUIDv4 random bits

ReadyUses the birthday approximation p ≈ 1 - exp(-n(n-1)/(2·2^122)). It estimates random collision probability, not implementation bugs or duplicated RNG state.

How to use this UUID Collision Probability Calculator

Estimate birthday-collision probability for UUIDv4 random identifiers with 122 random bits. Enter your values above and the result is calculated directly in your browser. No account is required.

Fast answer, clear inputs

This tool is built around one job: give the answer quickly without forcing a signup or hiding the result. Related tools are linked nearby when the next calculation or conversion is useful.