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Number base converter

Type a number in binary, octal, decimal, hex or any base from 2 to 36, and see it in all the others at once. Integers of any size stay exact.

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Worked example

The largest unsigned 64-bit integer, 2⁶⁴ − 1, written in decimal, hex and base 36.

decimal
18446744073709551615
hex · base 36
FFFFFFFFFFFFFFFF
3W5E11264SGSF

Common mistakes

  • Leaving a 0x prefix in a decimal field

    0x10 is 16, not 10. The converter tells you when a prefix doesn’t match the field you typed in.

  • Reading 010 as ten

    In some languages a leading 0 means octal, so 010 is 8. Here, leading zeros are ignored in every field, and octal is only octal in the octal field.

  • Trusting a spreadsheet with big numbers

    Spreadsheets and JavaScript numbers keep about 15–17 significant digits, so 64-bit IDs get rounded. This converter is exact at any length.

  • Mixing up the letter O and zero

    In bases above 24, O is a digit worth 24. Check the error message if a value looks wrong.

How it works

  1. 1

    Type in any field

    Binary, octal, decimal, hexadecimal, or the custom base. The other fields update as you type.

  2. 2

    Use the notation you have

    Prefixes like 0x, 0b and 0o, a minus sign, and underscores or spaces between digits are all accepted. An invalid digit is named, with its position.

  3. 3

    Copy the result

    Each field has a copy button. Turn on Group digits to read long binary in groups of 4 and hex in pairs.

Questions

How do I convert binary to decimal by hand?
Multiply each digit by 2 raised to its position, counting from 0 on the right, and add them up: 1011 is 8 + 0 + 2 + 1 = 11.
Why does each hex digit match four binary digits?
Because 16 is 2⁴. That makes hex a compact way to write binary: 1111 0000 is F0, and a byte is always two hex digits.
Is there a size limit?
No practical one. The converter uses JavaScript BigInt, so a 1,000-digit number converts exactly, unlike calculators that round after about 16 digits.
How are negative numbers shown?
With a minus sign in every base: -255 is -ff in hex. The converter doesn’t show two’s complement, because that depends on a fixed bit width.
Can it convert fractions?
No, only whole numbers. Fractions often have no exact form in another base: 0.1 in decimal repeats forever in binary.