UUID Collision Calculator
Calculate the probability of a collision when generating UUIDs, ULIDs, NanoIDs, or any unique string — based on the Birthday Problem.
Configuration
UUID v4 — 128-bit with 122 random bits (6 bits fixed for version/variant).
Collision AnalysisBased on Birthday Problem
Collision Probability
9.40 × 10^-26%
10.31 quadrillion
0.0001% chance
326.92 quadrillion
Caution zone
2.71 × 10^18
Birthday paradox
Bits of Entropy
122
Total Space
5.32 × 10^36
How It Works
The Birthday Problem tells us the probability that at least two values collide when drawing n items uniformly from a space of N possible values:
P(collision) ≈ 1 − e−n² / (2N)
For UUID v4 (122 bits), you would need to generate roughly 2.7 × 10¹⁸ UUIDs before hitting a 50% collision probability — far beyond any practical system.
Shorter identifiers (NanoID-10, UUID v7 within same ms) have fewer random bits and are more susceptible to collisions under heavy load.