Maybe I didn't look hard enough, but I couldn't find a generic, simple base translator that worked with floating point values (i.e. non-round numbers), so I made this. Weirdly, Javascript's native base conversion supports floating points in one direction but not the other. The ECMAScript spec is a bit ambiguous on this but I assume it's the same in all modern browsers.

Converting fractions may seem confusing at first but it's actually the same logic as whole numbers. When you have a number in base 10, say, 325.79, each digit tells you the multiple of a power of ten:

102	101	100	10-1	10-2
3	2	5	7	9
300	+   20	+   5	+   0.7	+   0.09	=   325.79

So you can see that the exponents of the base just carry on into negative numbers. I wonder why no one seems to bother.