UUID Collision Probability Calculator

Collision probability by identifier count

Step-by-step calculation

1. 1With 122 random bits the UUID space contains about 5.317e+36 values.
2. 2Generating 1,000,000,000 identifiers creates 5.000e+17 unordered pairs.
3. 3Dividing the pairs by the space gives an expected 9.404e-20 collisions and a 9.40e-20 chance of at least one.
4. 4The 50% birthday threshold is about 2,714,922,669,395,445,000 UUIDs; a 1e-12 risk is reached at about 3,260,954,456,334 UUIDs, or 1.03 years at 100,000 per second.

Round-trip verification

Best for: Escaping, encoding and permission conversions

• Method: Convert the value, decode it back with the target parser and compare the result with the original byte sequence.
• Precision: Test non-BMP characters, control characters, quotes, backslashes, newlines and an empty value.
• Safeguards: Escape at the output boundary and rely on the framework encoder rather than manual replacement.

Contract-first types

Best for: JSON-to-TypeScript, JSON-to-struct and SQL placeholder work

• Method: Collect several representative samples, infer the shape, then review optional fields, nulls and unions before committing the type or schema.
• Precision: Treat one sample as a lower bound on the real contract; add schema validation for runtime data.
• Safeguards: Run the generated types through CI and compare them with the next API revision.

Least-privilege configuration

Best for: Permissions, .env files, identifiers and dependency ranges

• Method: Choose the smallest permission set, keep secrets out of version control and pin or narrow version ranges deliberately.
• Precision: Account for the umask, the deployment platform limits and the full identifier lifetime.
• Safeguards: Audit world-writable files, setuid binaries, committed secrets and unpinned production dependencies.

Where each escape applies

Core relationship

P(collision) ≈ 1 − exp(−n(n−1) / (2 × 2^bits)); 50% threshold ≈ 1.1774 × 2^(bits/2)

Unit convention

Inputs are uuid variant, uuids generated, random bits (custom), target risk exponent, generation rate per second. Keep each unit consistent with the result rows; convert before comparing estimates that use different units or time windows.

Validation

1. Reproduce the headline from the displayed rows. 2. Compare the result with a measured, billed or benchmarked value. 3. Re-run with a boundary input and with a scaled input. 4. Record the assumptions, source and date next to the result.

One billion UUID v4 identifiers

Inputs

UUID variant = v4; UUIDs generated = 1000000000; Random bits (custom) = 122; Target risk exponent = 12; Generation rate per second = 100000

Math

P(collision) ≈ 1 − exp(−n(n−1) / (2 × 2^bits)); 50% threshold ≈ 1.1774 × 2^(bits/2)

Result

9.40e-20 collision risk · Variant: Version 4 · Random or unique bits: 122 · Address space: 2^122 ≈ 5.317e+36

One trillion UUID v7 identifiers

Inputs

UUID variant = v7; UUIDs generated = 1000000000000; Random bits (custom) = 74; Target risk exponent = 15; Generation rate per second = 1000000

Math

P(collision) ≈ 1 − exp(−n(n−1) / (2 × 2^bits)); 50% threshold ≈ 1.1774 × 2^(bits/2)

Result

100% collision risk · Variant: Version 7 · Random or unique bits: 74 · Address space: 2^74 ≈ 1.889e+22

Fifty million custom 64-bit IDs

Inputs

UUID variant = custom; UUIDs generated = 50000000; Random bits (custom) = 64; Target risk exponent = 9; Generation rate per second = 250000

Math

P(collision) ≈ 1 − exp(−n(n−1) / (2 × 2^bits)); 50% threshold ≈ 1.1774 × 2^(bits/2)

Result

6.78e-5 collision risk · Variant: Custom · Random or unique bits: 64 · Address space: 2^64 ≈ 1.845e+19

JavaScript / TypeScript

Use JSON.parse plus a schema validator, escape at the HTML or JSON output boundary, and let a semver library parse ranges instead of comparing strings. For uuid collision probability calculator, use the same units and time window described in the calculator so the result lines up with your platform data.

Python

Use json.dumps with ensure_ascii when an ASCII payload is required, os.chmod with an explicit mode, and packaging.version for PEP 440 or SemVer-aware comparisons. For uuid collision probability calculator, use the same units and time window described in the calculator so the result lines up with your platform data.

Shell and CI

Use printf %q for safe shell quoting, keep .env files out of the repository, verify modes with stat, and let the release tool write the version tag and package metadata together. For uuid collision probability calculator, use the same units and time window described in the calculator so the result lines up with your platform data.

SQL and ORMs

Use prepared statements for every value, compute batch size from the driver limit divided by placeholders per row, and log the parameter count when a bulk insert fails. For uuid collision probability calculator, use the same units and time window described in the calculator so the result lines up with your platform data.

Mistakes that break conversions

• Treating a low collision probability as a guarantee and skipping the unique constraint.
• Assuming version 1 UUIDs are random when they are mostly timestamp and node ID.
• Mixing units or time windows when comparing two uuid collision probability calculator results.
• Treating the default values as a recommendation instead of a starting point.
• Reporting a single number without the assumptions, range or measurement date behind it.

Pro tips for production code

• Estimate collisions over the total number of identifiers the system will ever create, not the current row count.
• Prefer version 4 or 7 for distributed IDs and keep version 3 or 5 for deterministic name-based keys.
• Measure the dominant input before refining the model; the largest uncertainty deserves the most attention.
• Keep a short record of the inputs, result and date so future comparisons are meaningful.
• Validate the estimate with a second method — a benchmark, a bill or production telemetry.
• Pair this result with the related calculators (UUID Generator / Validator, Birthday Attack Probability Calculator, Random Number Collision Probability Calculator) for a complete picture.