Convert numbers between any base from 2 to 36 — binary, octal, decimal, hex — using BigInt for exact arbitrary-size values. Private, in-browser, no uploads.
Runs entirely in your browser — your data never leaves your device.
How to use Number Base Converter
What it does & when you need it
Reading a permission bitmask in hex, decoding a color, checking an assembler
constant, or teaching yourself how binary works — sooner or later you need to move
a number from one base to another. This converter takes an integer written in any
base from 2 to 36 and rewrites it in any other, instantly and in your browser. It
uses BigInt under the hood, so even a value far larger than a normal calculator
can hold converts exactly, digit for digit, with no rounding.
How to use
Type or paste a number into the value buffer.
Set the From base (how the input is written) and the To base (what you
want out). The one-tap BIN / OCT / DEC / HEX buttons jump the output base
to the four common choices.
Read the converted value below and copy it with Copy result or
Ctrl/Cmd + Enter.
Things worth knowing
Any base from 2 to 36. Digits beyond 9 use the letters a–z, so hex runs
a–f and base 36 uses the whole alphabet. You are not limited to the familiar
four — base 5 to base 27 works just as well.
Big numbers stay exact. Because the math uses BigInt, there is no
2^53 safe-integer limit and no floating-point drift. A 40-digit decimal or a
long SHA hash in hex converts precisely.
Invalid digits are caught. A digit that is not legal for the from-base — a 2
in binary, or a g in hex — is flagged rather than silently ignored. Letter
digits are case-insensitive, so FF and ff both read as 255.
Signs and zeros. A single leading minus is preserved (-255 becomes -ff),
leading zeros and a leading plus are normalized away, and output letters are
lowercase — uppercase them afterwards if your format prefers FF. For color hex
values specifically, try the Color Converter.
Examples
Binary to hexadecimal
11111111 (base 2 → 16)
A full byte of 1s is 255, which is ff in hex.
Decimal to binary
42 (base 10 → 2)
The answer to everything, 42, is 101010 in binary.
Huge decimal to hex (BigInt)
18446744073709551616 (base 10 → 16)
2^64 is beyond a safe JS number, yet converts exactly to 10000000000000000.
Hex to base 36
ff (base 16 → 36)
Base 36 packs 255 into just two digits, 73, using the full a–z digit set.
Frequently asked questions
Which bases are supported?+
Any base from 2 to 36, in either direction. Digits above 9 use the letters a–z, so base 16 uses a–f and base 36 uses the full a–z. Binary, octal, decimal, and hexadecimal have one-tap buttons, but you can pick any pair, such as base 5 to base 27.
Can it convert numbers too large for a normal calculator?+
Yes. The conversion uses JavaScript's BigInt, so there is no 2^53 safe-integer ceiling and no floating-point rounding. A 40-digit decimal or a long hexadecimal hash converts to its exact value in the target base with every digit preserved.
What counts as a valid digit, and is it case-sensitive?+
Only digits legal for the from-base are accepted; entering 2 while converting from binary, or g while converting from hex, is flagged as an invalid digit. Letter digits are case-insensitive, so FF and ff both read as 255 from base 16.
Does it handle negative numbers and leading zeros?+
A single leading minus sign is carried through the conversion, so -255 from base 10 becomes -ff in base 16. Leading zeros and a leading plus sign are accepted and normalized away, and negative zero collapses to a plain 0.
Is hexadecimal output upper or lower case, and does this work offline?+
Output uses lowercase letters for digits above 9 (ff, not FF); uppercase it afterwards if your format needs it. The whole conversion runs locally in your browser with no network request, so it keeps working offline once the page has loaded.