IP address to binary converter

How do you convert an IP address to binary?

An IPv4 address is a 32-bit number; RFC 791 defines addresses as a fixed four octets. Dotted decimal writes each 8-bit octet as a number from 0 to 255, so converting to binary means writing each of the four numbers as exactly 8 bits and keeping the dots: 192 is 11000000, 168 is 10101000, 1 is 00000001 and 10 is 00001010.

To convert one octet by hand, take the place values 128, 64, 32, 16, 8, 4, 2 and 1 from the left. Write 1 under each value you can subtract from what is left of the number, and 0 under the rest: 168 is 128 + 32 + 8, so it is 10101000. Always keep all eight digits, including the leading zeros, or the bits of the next octet shift into the wrong places.

The same 32 bits can be read as one number: the first octet × 256³ + the second × 256² + the third × 256 + the fourth, so 192.168.1.10 is 3,232,235,786. That is the integer MySQL's INET_ATON() returns, and the form to store in an unsigned 32-bit column. In hex, each octet is two digits: 192.168.1.10 is 0xC0A8010A.

This converter refuses parts with leading zeros, such as 192.168.010.1. The C library's inet_aton reads a part that starts with 0 as octal, so 010 is 8 there, not 10; Python's ipaddress module has rejected leading zeros since version 3.9.5 to avoid that confusion. Short forms such as 127.1, which inet_aton accepts as 127.0.0.1, are also refused: write all four octets.

place values:  128 (2⁷)  64 (2⁶)  32 (2⁵)  16 (2⁴)  8 (2³)  4 (2²)  2 (2¹)  1 (2⁰)
192 = 128 + 64             →  11000000
168 = 128 + 32 + 8         →  10101000
192.168.1.10  →  11000000.10101000.00000001.00001010
as one number = 192 × 256³ + 168 × 256² + 1 × 256 + 10 = 3,232,235,786