Hash Collision Probability Calculator

Calculate the probability that at least two items produce the same hash value (a collision), given the number of possible hash values and how many items are hashed — an application of the birthday paradox to hash functions.

Inputs

e.g. 2^32 = 4294967296 for a 32-bit hash

Results
Collision Probability
1.1573

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Formula

P(collision) = 1 − ∏ᵢ₌₀ⁿ⁻¹ (N − i) / N, where N = hash space size, n = items hashed

Learn How This Works

Security and API Planning: Entropy, Rate Limits, and Collisions

Password entropy, URL query parameter counting, hash collision probability, and API rate limits — four calculations for planning secure, well-behaved systems.

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