Number Base Converter
Convert numbers between binary, decimal, hexadecimal, and octal, at any size, in your browser. Byte-grouped binary included.
Private by construction. The conversion happens in this page's JavaScript. Nothing you paste here leaves your machine, and the tool keeps working with the network unplugged.
Paste a number in any of the four programmer bases — decimal, hex (0x), binary (0b), or octal (0o) — and read off all of them at once, plus a byte-grouped binary view and the bit length. Conversion uses arbitrary-precision integers, so 64-bit values, 256-bit hashes, and anything else convert exactly; there is no silent precision loss at 2⁵³, which is where converters built on ordinary JavaScript numbers start quietly corrupting results. Underscores and spaces in the input are ignored, so 0xdead_beef pastes straight from source code.
Questions this tool gets asked
Why does bare “ff” give an error instead of converting from hex?
Because “ff” could be hex or a typo, and guessing corrupts data. The prefixes 0x, 0b, and 0o make the base explicit, the same convention every modern language uses.
How large a number can this handle?
Effectively unlimited - conversion uses BigInt arithmetic, so 256-bit hashes and larger convert exactly. Converters that use ordinary floating-point numbers silently round anything above 9,007,199,254,740,991.
How are negative numbers shown in binary?
As a minus sign and the magnitude, not as two's complement, because two's complement is only meaningful at a fixed bit width, and this tool doesn't guess one. The bit count shown is of the magnitude.
What is the “bytes” line?
The same binary value, zero-padded to whole bytes and grouped 8 bits at a time - the way you would read it in a hex dump or when working out masks and flags.