An exhaustive converter.

Its got it all. But a bit cumbersome.
I use Milas Tools for the handful of conversions I normally need. I keep this app handy for the huge variety of unit conversions it provides, and some of them are a bit arcane, like shoe sizes and typography (but handy when you need them.
Decimal to hexadecimal-where was that when I was learning BASIC?

Dent De Leon about Convert ~ the unit calculator, v2.0.2