Number Base Converter
Processed Client SideConvert numbers between binary, octal, decimal, and hexadecimal with full BigInt precision.
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About Number Base Converter
This tool runs entirely in your browser. Whatever you paste is processed on your own device and is never uploaded, logged, or sent to any server.
Convert a number between binary, octal, decimal, and hexadecimal, and see all four representations at once. Pick the base your input is written in, type the number, and every other base updates immediately, with the conventional prefixes — 0b, 0o, 0x — and digit grouping that makes long values readable. Conversion is done with arbitrary-precision integers, so values far beyond the range where floating-point arithmetic starts silently rounding are still exact. That matters for the things developers actually convert: 64-bit flags, permission masks, colour values, and memory addresses. Prefixes and grouping separators in your input are ignored rather than rejected, so a value copied back out of the tool, or straight out of a debugger, can be pasted in as it stands.
Key features
- Binary, octal, decimal, and hexadecimal shown together — change the input and all four update
- Arbitrary-precision arithmetic using BigInt, so very large values stay exact instead of rounding
- Conventional prefixes on the output: 0b for binary, 0o for octal, 0x for hexadecimal
- Digit grouping — binary and hex in groups of four, decimal in thousands — so long numbers stay readable
- Input base selector for binary, octal, decimal, and hex
- Invalid digits are reported precisely, naming the character that is not valid in the chosen base
- Preset values for common starting points — 255, 0xFF, and the byte and word boundaries, each preloaded with its own base
- Input tolerant of 0x prefixes and grouping spaces, so a value can be pasted back in exactly as it was displayed
- Each base shown on its own card, grouped for reading, with the prefixed form available to copy
- Runs entirely in your browser with no size limit imposed by a server
How to use it
- Choose the base your number is currently written in.
- Type or paste the number.
- Read the binary, octal, decimal, and hexadecimal results side by side.
- Copy whichever representation you need.
Tips & common mistakes
- One hex digit is exactly four binary digits, which is why hex is the shorthand for bit patterns — 0xFF is 11111111 and needs no arithmetic to see.
- Octal survives mainly in UNIX file permissions: 0755 is rwxr-xr-x because each octal digit encodes exactly three permission bits.
- Because this uses BigInt, values beyond 2^53 stay exact. Ordinary JavaScript number arithmetic starts losing integer precision above that point.
- Colour work is base conversion in disguise: #FF8000 is three bytes, and reading them as 255, 128, 0 is what the RGB tools do for you.
- An "invalid digit" error usually means a stray prefix or separator — strip the 0x, 0b, or spaces, or switch the input base to match what you actually pasted.
- Negative numbers in binary are normally stored as two-complement in a fixed width, so a raw conversion here will not match what a debugger shows for a negative 32-bit int.
- The displayed value is grouped for reading and the copied value carries its prefix instead. That is deliberate — grouped digits are easier to check by eye, and the prefixed form is what a compiler or a REPL will accept.
- Leading zeros carry no value here, so 0755 and 755 in base 8 convert identically. In source code the leading zero is what marks a literal as octal, which is a difference worth keeping in mind when you paste a result back into a file.