Convert Base Numbers Online
Convert Base Numbers between bases 2-36 (binary, octal, decimal, hex). Arbitrary precision via BigInt. Free, client-side, instant, secure.
Convert integers between any two bases from 2 to 36, with arbitrary precision — your numbers never leave the browser.
How to Use Convert Base Numbers Online
- Type or paste your number into the input field. Accepts any integer written in the selected "From base" - including a leading minus sign for negatives.
- Set the "From base" to match how your number is currently written. Use the
Bin/Oct/Dec/Hexpreset buttons for the common cases. - Set the "To base" to the radix you want to convert into. Any integer from 2 through 36 works; bases above 10 use letters A-Z as digits.
- Press
Convertor hitCtrl+Enter(⌘+Enteron Mac). The result and its decimal equivalent appear immediately, with a stats line showing digit and bit counts. - Use
⇄ Swapto reverse the direction - the output becomes the new input so you can round-trip and verify. - Fix any typos - if you enter a character that is not legal for the chosen base, the error block names the offending digit so you know exactly where the problem is.
- Copy the result to your clipboard or Download it as a timestamped `.txt` file that also records the decimal value and bit length.
Frequently asked questions
Which bases are supported?
Every integer base from 2 (binary) through 36. The digits used are 0-9 followed by A-Z, so a base-36 digit can be anything from 0 to Z.
Is my number sent to a server?
No. The conversion runs entirely in your browser using JavaScript BigInt. There is no fetch, no XHR, and no analytics on your input – the page works fully offline after it loads.
Does it handle numbers larger than 2^53?
Yes. The tool uses native BigInt for parsing and formatting, so 256-digit hex numbers and multi-thousand-bit decimals convert exactly without precision loss.
Are negative numbers supported?
Yes. Prefix the input with a minus sign (for example -FF base 16 → -11111111 base 2). The sign is preserved across any base conversion.
What happens if I type an invalid digit?
The tool rejects the input and names the offending character – for example, “Invalid digit ‘G’ for base 10”. Unlike a plain parseInt, it never silently drops characters it does not recognise.
Is case sensitive?
No. ff, FF, and Ff at base 16 all convert to the same value. The output is always uppercase for clarity.
Does it show the decimal equivalent?
Yes – below the primary result the tool shows the exact decimal (base 10) value, so you always have a familiar reference point.
Can I swap the From and To bases quickly?
Yes. The ⇄ Swap button swaps the two bases and feeds the previous output back in as the new input, making round-trip verification a single click.
What are the Bin / Oct / Dec / Hex buttons for?
They are one-click presets that set the adjacent base field to 2, 8, 10, or 16 respectively. Handy for the 90 % of conversions that only use the common radixes.
Is there a size limit?
Only your browser’s memory. Conversions of thousand-bit numbers finish in milliseconds, and the tool has no artificial character cap on the input.