CRC-16/CCITT Checksum Calculator

About this calculator

CRC-16/CCITT-FALSE runs a message through polynomial division using the generator polynomial 0x1021 (x¹⁶+x¹²+x⁵+1) with a non-zero initial register value of 0xFFFF, producing a 16-bit remainder that acts as a checksum. The non-zero init distinguishes it from the plainer CRC-16/CCITT (init 0x0000) and lets it catch leading-zero errors that a zero-init variant would miss.

This exact variant is what protocols like XMODEM/CRC, Bluetooth's HCI layer, and many industrial serial links use to detect transmission errors, so firmware and protocol engineers need a calculator that matches the specific polynomial and initial value rather than a generic “CRC-16.”