Number Base Converter

The conventional prefixes are recognised for the base you choose: 0x for hexadecimal, 0b for binary and 0o for octal. A leading minus sign makes the number negative.

Spaces, commas and underscores are ignored, so 1111_0000, 1111 0000 and 11110000 are the same number. Letters are not case-sensitive. Bases above 10 use the letters of the alphabet for the extra digits, which is why base 16 stops at f and base 36 stops at z.

JavaScript numbers are 64-bit floating-point values, and they hold whole numbers exactly only up to 9,007,199,254,740,991. Above that, a converter built on ordinary numbers rounds without telling you:

Those are the largest unsigned and signed 64-bit integers, which is exactly where hashes, identifiers and bit masks tend to live. This tool does its arithmetic on big integers, so every digit is right at any size.

Computers store negative integers in two's complement: invert every bit of the positive value and add one. The same bit pattern is a different number depending on how wide the integer is.

• -1 is 11111111 (0xFF) in 8 bits, 0xFFFF in 16 bits and 0xFFFFFFFF in 32 bits.
• -128 is 10000000 in 8 bits, the lowest value an 8-bit signed integer holds.

The table shows the pattern at every standard width that can hold the value. A width is left out when the number does not fit it, because 128 is simply not a signed 8-bit value.

• One hex digit is exactly four bits, so a byte is always two hex digits. That is why hex is used to write binary data.
• One octal digit is exactly three bits, which is why Unix permissions are written in octal. See the chmod calculator.
• 0xFF is 255, 0x7FFFFFFF is 2,147,483,647 (the largest signed 32-bit integer) and 0xFFFFFFFF is 4,294,967,295.
• A Unix timestamp of 2,147,483,647 is the last second a signed 32-bit clock can count.