MurmurHash3 is a fast non-cryptographic hash by Austin Appleby, designed for excellent distribution and speed. The 32-bit variant computed here is widely used in hash tables, bloom filters and sharding.

Which MurmurHash3 variant does this compute?

It computes MurmurHash3_x86_32, the 32-bit little-endian variant. This is the most common form referenced simply as MurmurHash3 in libraries and databases.

What does the seed do?

The seed initialises the hash state, so the same input produces different outputs for different seeds. Use a fixed seed when you need reproducible hashing, and vary it for independent hash functions.

How are leftover tail bytes handled?

MurmurHash3 processes the input in 4-byte blocks; the remaining 1 to 3 bytes are mixed in a separate tail step before the final avalanche (fmix32). This tool implements that tail handling exactly.

Is MurmurHash3 cryptographically secure?

No. MurmurHash3 is fast and well-distributed but not collision-resistant against an attacker. Use it for data structures, not for passwords, tokens or signatures.

MurmurHash3 Calculator

MurmurHash3 is a fast, high-quality non-cryptographic hash function used throughout databases, caches and probabilistic data structures. This calculator implements the 32-bit x86 variant (MurmurHash3_x86_32) with a configurable seed, computing everything locally in the browser.

How it works

The algorithm mixes the input in 4-byte little-endian blocks, then finalises:

Initialise the hash with the seed and set the constants c1 = 0xcc9e2d51, c2 = 0x1b873593.
For each 4-byte block k: multiply by c1, rotate left 15, multiply by c2, XOR into the hash, rotate the hash left 13, then set hash = hash * 5 + 0xe6546b64.
Mix any leftover 1 to 3 tail bytes through the same c1/rotate/c2 step.
XOR the total length into the hash, then run the finalisation mixer fmix32 (a sequence of shifts, XORs and multiplications) to avalanche the bits.

Example

Hashing hello with seed 0 produces 0x248bfa47 (decimal 613153351). An empty string with seed 0 hashes to 0.

Notes

All multiplications use a correct 32-bit overflow multiply so results match reference C implementations bit for bit. MurmurHash3 is excellent for hash tables but offers no security guarantees. Every computation runs locally and nothing is uploaded.