How does Fletcher-32 differ from Fletcher-16?

Fletcher-32 processes the data as 16-bit words instead of bytes and uses modulus 65535 instead of 255. This widens the checksum to 32 bits and gives stronger detection of larger burst errors.

What happens with an odd number of bytes?

The standard pads a trailing lone byte with a zero high byte so it still forms a complete 16-bit word. This tool follows that convention, so any byte length is accepted.

How is the 32-bit value assembled?

The high 16 bits are sum2 and the low 16 bits are sum1, so the checksum equals (sum2 << 16) | sum1. The tool shows both word components for verification.

Can I input raw bytes as hex?

Yes. Choose Hex bytes mode and enter pairs of hex digits, optionally separated by spaces or commas. An even number of hex digits is required.

Is Fletcher-32 cryptographically secure?

No. Like all Fletcher variants it is an error-detection checksum, not a secure hash. Use it for catching accidental corruption, never for security purposes.

Fletcher-32 Checksum Calculator

Q: Can I input raw bytes as hex?

Yes. Choose Hex bytes mode and enter pairs of hex digits, optionally separated by spaces or commas. An even number of hex digits is required.

Q: Is Fletcher-32 cryptographically secure?

No. Like all Fletcher variants it is an error-detection checksum, not a secure hash. Use it for catching accidental corruption, never for security purposes.

The Fletcher-32 checksum extends Fletcher-16 to a 32-bit result by working on 16-bit words and reducing its two running sums modulo 65535. The wider accumulator detects larger and more complex burst errors while remaining inexpensive. This calculator runs the standard algorithm locally over text or hex bytes.

How it works

Fletcher-32 keeps two running sums, both reduced modulo 65535:

Start with sum1 = 0 and sum2 = 0.
Read the data two bytes at a time into a 16-bit word w = (high << 8) | low.
For each word: set sum1 = (sum1 + w) mod 65535, then sum2 = (sum2 + sum1) mod 65535.
The final checksum is (sum2 << 16) | sum1.

If the data has an odd number of bytes, the last byte is padded with a zero high byte so it still forms one complete word.

Example

For the ASCII string abcde the algorithm produces the checksum 0xF04FC729. Enter it in the tool to confirm the same hex and decimal output.

Notes

The modulus 65535 (2^16 - 1) plays the same role as 255 does in Fletcher-16: it keeps the sums position-sensitive so byte and word swaps are detected. Fletcher-32 is a data-integrity check only and does not defend against intentional tampering. All computation runs in your browser.