CRC Calculator: CRC-8, CRC-16, CRC-64 & Modbus

A CRC is fully described by six numbers — width, polynomial, initial value, whether input bytes are reflected, whether the result is reflected, and a final XOR — and this calculator takes any combination of them for widths from 1 to 64 bits. It also carries all 112 CRCs of 64 bits or fewer in Greg Cook's reveng catalogue under their catalogue names and common aliases, so CRC-16/MODBUS, CRC-16/CCITT-FALSE (IBM-3740), XMODEM, KERMIT, X-25, CRC-8/MAXIM, CRC-32/MPEG-2, CRC-32C and CRC-64/XZ are one choice away. Input can be UTF-8 text, hex bytes or a file up to 64 MB. The result is shown in hex, decimal and binary, and for whole-byte widths also as the bytes in both orders: Modbus RTU, for instance, transmits its CRC low byte first, so 0x4B37 goes on the wire as 37 4B. Every line also shows the CRC of the ASCII string 123456789, which is the 'check' value data sheets and the catalogue quote, so a custom setting can be confirmed against documentation before it is trusted. The table below runs every catalogued CRC over the same input, and typing a value you observed filters it to the presets that produce it, byte-swapped matches included. One sample is rarely enough to identify an unknown CRC — with 16-bit CRCs a random match turns up in about one case in 65,536 per preset — so confirm with a second message. Messages are whole bytes; CRCs over a bit count that is not a multiple of 8, and the 82-bit CRC-82/DARC, are outside its scope. A CRC detects accidental errors and is not a security measure: anyone can recompute it after changing data.