UUID Collision Calculator

Approximate the collision probability for randomly generated UUID v4 identifiers.

A standard UUID v4 has 122 random bits after version and variant fields.

About the UUID Collision Calculator

This tool estimates how likely at least one duplicate is among independently and uniformly generated UUID v4 values.

How to use it

  1. Enter the number of UUIDs that will be generated.
  2. Keep UUID v4 selected and use 122 random bits for the standard format.
  3. Calculate to see an approximate probability and risk label.

Birthday approximation

The estimate uses p ≈ 1 - exp(-n(n - 1) / (2 × 2^b)), where n is the generated count and b is the random-bit count.

Example

Even one billion standard UUID v4 values have an extremely small approximate collision probability because the random space contains 2^122 possibilities.

Assumptions

The formula assumes independent, uniformly random generation. Weak random-number generators or implementation defects are not represented by the mathematical estimate.