Number Base Converter

A Number Base Converter rewrites the same integer in a different positional notation. The value does not change - 255, 0xFF, 0o377, and 0b11111111 are four spellings of one quantity - only the radix used to write it down changes. This tool converts between any two bases from 2 to 36, with binary, octal, decimal, and hexadecimal treated as first-class citizens because those are the four you meet in code.

Conversion works digit by digit. Reading a number in base b means accumulating `value = value * b + digit` across the input; writing it back out in base c means repeatedly dividing by c and collecting remainders. This tool performs both halves in BigInt arithmetic, so a 64-bit hash, a 256-bit key, or a 500-digit decimal is converted exactly. Nothing is routed through a JavaScript number, which would silently lose precision above 2^53.

Alongside the conversion you get the measurements that usually prompt the question in the first place: how many significant bits the value occupies, how many bytes it needs, and the binary form grouped into nibbles so you can read it against a hex digit. Negative values are supported, common literal prefixes (0x, 0b, 0o) are accepted, and underscores or spaces can be used as digit separators. Everything runs in your browser.

A good test for any number base converter online is the largest unsigned 64-bit value. Type 18446744073709551615 with the source set to Decimal and the target to Base 36. The To box shows 3W5E11264SGSF, and the all-bases table lists FFFFFFFFFFFFFFFF in hexadecimal and 64 ones in binary, with a bit length of 64 and a byte length of 8. A base number converter that routes the value through a floating-point number would get the low digits wrong here; this number base converter calculator does not.

Arithmetic here uses arbitrary-precision integers rather than JavaScript numbers, which is the difference between a correct answer and a plausible one. A standard double loses precision above 9007199254740991, so a 64-bit hexadecimal value converted through ordinary floating point comes back subtly wrong in its lower digits, and nothing warns you. Two scope notes. This converts integers, so fractional values in a base other than ten are outside what it does. And negatives are shown with a minus sign rather than as a two's complement bit pattern, so a value read from a register or a memory dump needs interpreting according to its width before conversion rather than after.