Why write another unit converter? There are plenty of them out there. Well, I couldn't find one that worked quite the way I wanted.
With ConvertAll, you can combine the units any way you want. If you want to convert from inches per decade, that's fine. Or from meter-pounds. Or from cubic nautical miles. The units don't have to make sense to anyone else.
See the ConvertAll homepage for more info.
There is also an online version that can be used with no software installation.