Decimal to Binary

A decimal to binary converter takes an ordinary base-10 number and rewrites it in base 2, the language of 0s and 1s that computers use internally. The standard method is repeated division by two: divide the number by 2, record the remainder, repeat with the quotient, and read the remainders from bottom to top. The number 13 becomes 1101 this way, because 13 = 8 + 4 + 0 + 1. This tool performs that conversion instantly for any integer and shows the binary string, so you can produce a bit pattern for a mask, check a homework answer, or set a configuration flag without grinding through the long division yourself. For negative numbers it shows the two's complement representation, which is how nearly all modern processors store signed integers. Two's complement is not simply the positive value with a minus sign attached: to encode -5 in 8 bits, you take the binary of 5, which is 00000101, invert every bit to 11111010, and add 1 to get 11111011. The result depends on the bit width, because the same negative number needs more leading ones in a wider field, which is why context about the byte or word size matters when you compare results across tools. The converter handles whole numbers only; fractional decimals such as 0.1, which famously have no exact finite binary representation, are not supported. Conversions stay exact up to JavaScript's safe-integer limit of 2 to the 53 minus 1. Everything runs locally in your browser, so nothing you enter is uploaded or logged. Pair it with the Binary to Decimal tool to convert in the opposite direction and confirm a value round-trips correctly.