One's Complement Calculator Bitwise NOT (flip all bits). Decimal Bits One's complement (decimal) 213 Binary 11010101 Step-by-step with your numbers: 1. Values used: 2. Decimal = 42 3. Bits = 8 4. One's complement (decimal) = 213 5. Binary = 11010101 Did we solve your problem today? 👍 Yes 👎 No Thanks for the feedback! Flip every bit (1→0, 0→1). FAQ Two's complement? One's + 1 = two's complement. Related calculators Two's Complement Calculator Signed representation of a decimal. Bitwise Calculator Find AND, OR and XOR of two numbers. Binary Addition Calculator Add two decimal numbers in binary.