CRC-32 checksum calculator

What CRC-32 does

A cyclic redundancy check is an error-detecting code. CRC-32 treats the data as a long binary polynomial, divides it by a fixed 33-bit polynomial and keeps the 32-bit remainder. It is fast in hardware and software and catches the errors that matter for storage and transmission: any single flipped bit, any two flipped bits, and every burst of errors up to 32 bits long. ZIP and gzip store a CRC-32 of each file, PNG has one per chunk, and Ethernet frames end with one.

CRC-32 is not a security hash. Changing data to match a given CRC is easy, so use SHA-256 when tampering is a concern.

Worked example

The standard check value: the CRC-32 of the nine characters 123456789 is cbf43926 in hex, 3,421,780,262 in decimal. Every correct implementation of this variant produces it, which makes it a handy way to confirm which CRC-32 a tool uses.

Variants

This page computes CRC-32/ISO-HDLC, the one in ZIP, gzip, PNG and Ethernet. CRC-32C (Castagnoli), used by iSCSI, ext4 and Google's storage APIs, uses a different polynomial and gives different results.

The text is encoded as UTF-8 and fed byte by byte through the CRC-32 algorithm specified in RFC 1952 (the gzip format): the register starts at all ones, each byte is combined with the register through a 256-entry table derived from the reflected polynomial 0xEDB88320, and the result is inverted at the end. The checksum is shown as eight hex digits and as an unsigned decimal number. The implementation is checked against the standard check value on every build. Nothing leaves your browser.