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Estimate collision probability for hash keyspaces with random-distribution assumptions. Compare risk thresholds and plan safer hash widths using our programming tools.
Last updated: April 14, 2026
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Collision Probability
2.71e-6%
Expected Collision Pairs
2.711e-8
~1% Collision Threshold
608,926,881 items
~50% Collision Threshold
5,056,937,541 items
Uses the standard approximation for practical collision-risk forecasting.
Shows safe scale regions and where collision risk accelerates.
Useful for designing IDs, fingerprints, and deduplication keys.
For 64-bit hashes and 1,000,000 items:
Collision Probability
~0.000003%
Expected Pairs
~2.7e-8
This calculator uses the birthday paradox approximation to estimate collision chance in a finite hash keyspace. It models how collision risk grows with the number of items relative to hash width.
P(collision) ≈ 1 - exp(-n(n-1)/(2 × 2^b))n = hashed items, b = hash bitsexpected pairs ≈ n(n-1)/(2 × 2^b)Pair this with our time complexity calculator and modulo calculator for stronger algorithm design workflows.
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Suggested hashtags: #Hashing #Security #BirthdayParadox #Algorithms #Programming #Calculator