Generate FNV-1a or FNV-1 32-bit and 64-bit non-cryptographic hashes from text or files up to 2 GiB each, with the offset basis and prime for each width.
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Pasted text up to 100 MiB, read as UTF-8, or files up to 2 GiB each.
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FNV is a family of small, fast, non-cryptographic hashes named after Glenn Fowler, Landon Curt Noll, and Kiem-Phong Vo. This tool offers FNV-1 and FNV-1a at both 32-bit and 64-bit widths.
FNV-1 and FNV-1a differ by exactly one thing: the order of two operations. FNV-1 multiplies the running hash and then XORs in the next byte. FNV-1a XORs first and then multiplies.
That single swap produces entirely different values, and the two are not interchangeable. FNV-1a is generally the one people mean and the one with better distribution on short inputs.
Tip
If you are matching an existing system, read its documentation carefully. The names differ by two characters, and the failure mode is a hash that simply never matches.
Every FNV hash starts from an offset basis and multiplies by an FNV prime, and both depend only on the width. FNV-1 and FNV-1a use the same pair, and RFC 9923 suggests FNV-1a for general use.1
| Width | Offset basis | FNV prime |
|---|---|---|
| 32-bit | 0x811C9DC5 | 0x01000193 |
| 64-bit | 0xCBF29CE484222325 | 0x00000100000001B3 |
To check an implementation, hash these inputs as UTF-8 and compare the hex output.
| Input | FNV-1a 32-bit | FNV-1a 64-bit | FNV-1 32-bit | FNV-1 64-bit |
|---|---|---|---|---|
a | e40c292c | af63dc4c8601ec8c | 050c5d7e | af63bd4c8601b7be |
foobar | bf9cf968 | 85944171f73967e8 | 31f0b262 | 340d8765a4dda9c2 |
MurmurHash3, SipHash and wyhash have better distribution and are the modern choice for hash tables. SipHash in particular is keyed, which protects a table against deliberately colliding keys.
CRC-32 and Adler-32 are the tools for detecting corruption. For anything cryptographic, use BLAKE3, SHA3 or SHA-256.
FNV's appeal is that it is almost nothing: a multiply and an XOR per byte, no tables, no setup, a few lines in any language. That is why it turns up embedded in file formats and small systems where pulling in a hash library would be absurd.
Warning
FNV is not cryptographic and must not be used for passwords, signatures, authentication, or integrity against an attacker. Anyone can find inputs that collide.
RFC 9923, The FNV Non-Cryptographic Hash Algorithm, IETF, February 2026. ↩
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