Ones Complement Calculator

About this calculator

The one's complement of a binary number is found by flipping every bit within a fixed width — every 0 becomes a 1 and every 1 becomes a 0. For example, the one's complement of the 8-bit value 00101100 is 11010011. This is different from two's complement, which is the one's complement plus 1, and which is what almost all modern processors actually use to represent negative numbers.

Older computer architectures, including some early mainframes and minicomputers, used one's complement directly to represent signed integers, which has the quirk of producing two different bit patterns for zero (positive zero and negative zero). One's complement arithmetic survives today mainly in the Internet checksum algorithm defined in RFC 1071, which computes IP, TCP and UDP header checksums using one's-complement addition specifically because it has useful properties for detecting bit errors and wraps around cleanly.

Enter a binary number and the calculator flips every bit to show you its one's complement instantly.