Number Base Converter
Converts a whole number between binary, octal, decimal, hexadecimal and any base from 2 to 36 — in your browser, with nothing sent anywhere.
Why this one is exact and most are not
Almost every base converter on the web is built on JavaScript's parseInt, and parseInt returns an ordinary number — a floating-point value that cannot hold whole numbers larger than about 9 quadrillion (2⁵³). Past that point it rounds, and gives you a wrong answer with total confidence. Convert ffffffffffffffff from hex on one of those tools and it will say 18446744073709552000; the real value is 18446744073709551615, off by 385.
This converter uses big integers instead, so it is exact for a number of any size. When the naïve answer would differ, it shows you both — the correct value and the wrong one those other tools would give — so the difference is something you can see, not just a claim we make.
Whole numbers only, and we say why
It converts integers, not fractions. That is not laziness: 0.1 in decimal is 0.0001100110011… repeating forever in binary, so any tool that shows you a few digits has quietly chosen where to stop and rounded. Rather than hand you a cutoff dressed up as an answer, this tool declines and tells you why. A bad digit is refused too, pointing at exactly which character and where. As always, the page is static and works offline, verified by our automated tests on every release.