What's the difference between FNV-1 and FNV-1a?

They perform the exact same two operations, multiply by the FNV prime and XOR with the next input byte, just in reversed order. FNV-1 multiplies first, then XORs; FNV-1a XORs first, then multiplies. That small reordering gives FNV-1a noticeably better avalanche behavior (small input changes spread more evenly through the output), which is why FNV-1a is the more commonly recommended variant of the two today.

Is FNV-1 cryptographically secure?

No, not even close, and it was never intended to be. FNV was designed by Glenn Fowler, Landon Curt Noll, and Kiem-Phong Vo specifically for fast, good-distribution hashing in hash tables and similar non-adversarial data structures, not to resist a deliberate attacker trying to construct collisions.

Where did FNV come from?

It originated from an idea the two authors described in an email exchange in 1991, and it's been used in a wide range of Unix and BSD system utilities since, DNS implementations, various programming language standard library hash-table implementations, and countless smaller tools that just need a fast, decent-quality hash without any cryptographic overhead.

Does this tool send my text to a server?

No. FNV-1 is computed entirely client-side in JavaScript, so nothing you type here is transmitted anywhere.

FNV-1 Hash Calculator - Calculate FNV-1 (32-bit) Online

Overview

Introduction

FNV-1 is one of the simplest hash functions in wide practical use: a running value repeatedly multiplied by a fixed prime and XORed with each input byte, fast enough to compute inline and good enough to spread keys evenly across a hash table.

This tool computes the 32-bit FNV-1 hash of any text you provide, entirely in your browser, for reproducing hash table bucket assignments or matching systems that specifically use the FNV-1 (rather than FNV-1a) ordering.

What Is FNV-1 Hash Calculator?

FNV-1 (Fowler/Noll/Vo, version 1) is a non-cryptographic hash function first described in 1991, producing a 32-bit result in this tool, shown as 8 hexadecimal characters, from a simple loop of multiply-then-XOR operations.

It belongs to the FNV family, which also includes FNV-1a (a reordered variant with better distribution) and 64-, 128-, and larger-bit versions defined by the same core algorithm at different word sizes.

How FNV-1 Hash Calculator Works

Starting from the 32-bit FNV offset basis (0x811c9dc5), each byte of your UTF-8 encoded text updates the running hash by first multiplying it by the FNV prime (0x01000193, mod 2^32), then XORing in the next byte.

After processing every byte, the final 32-bit value is hex-encoded into the 8-character output this tool returns.

When To Use FNV-1 Hash Calculator

Use FNV-1 specifically when reproducing a value from a system that already uses the FNV-1 (multiply-then-XOR) ordering rather than FNV-1a.

For a new hash table or general-purpose non-cryptographic hashing need without that specific compatibility requirement, FNV-1a is generally the recommended variant, its reordered operations give measurably better bit distribution.

Often used alongside FNV-1a Hash Calculator and MurmurHash3 Calculator.

Features

Advantages

Extremely simple and fast to compute, just a multiply and an XOR per byte.
Good, well-understood distribution properties for hash table use.
Long track record in Unix/BSD system tooling and various language standard libraries.

Limitations

Not cryptographically secure; trivial to construct deliberate collisions.
FNV-1a generally offers better avalanche behavior than FNV-1's multiply-then-XOR ordering.
32-bit output is prone to accidental collisions on larger datasets (the birthday bound applies well before 2^32 items).

Examples

Hashing a short greeting

Input

Hello, world!

Output

e84ead66

13 bytes of UTF-8 text produce the standard 8-character 32-bit FNV-1 hash.

Hashing a well-known FNV reference string

Input

foobar

Output

31f0b262

This exact value is a commonly cited 32-bit FNV-1 test vector, useful for confirming any implementation matches the standard.

Best Practices & Notes

Best Practices

Choose FNV-1 only to match an existing system already using that exact ordering; otherwise prefer FNV-1a for its better distribution.
Never use FNV-1 (or any FNV variant) where security against deliberate collisions matters.
For hash tables where distribution quality is critical and there's no legacy constraint, also consider MurmurHash3 or xxHash, both offer stronger statistical distribution in most benchmarks.

Developer Notes

This tool implements the 32-bit FNV-1 algorithm directly per the IETF draft specification (offset basis 0x811c9dc5, prime 0x01000193, multiply-then-XOR per byte), verified against published FNV-1 test vectors including the empty string and "foobar".

FNV-1 Hash Calculator Use Cases

Reproducing a hash table bucket assignment from a system using classic FNV-1 ordering
Matching a checksum or identifier from Unix/BSD tooling or a language standard library that uses FNV-1
Reproducing a known FNV-1 test vector while debugging another implementation
Fast, non-adversarial hashing where a simple, well-understood algorithm is preferred

Common Mistakes

Using FNV-1 where FNV-1a was intended; the two produce different output for the same input due to their reversed operation order.
Assuming FNV-1 provides any resistance to deliberate hash collisions; it doesn't, by design.
Choosing FNV-1 for a brand-new hash table without checking whether FNV-1a's better distribution would serve better.

Tips

If you don't have a specific reason to need FNV-1's exact ordering, use the FNV-1a tool instead, it's the generally recommended variant.
For hash table use where distribution quality is critical, also benchmark MurmurHash3 or xxHash against FNV before committing.

FNV-1 Hash Calculator