From Abhisoft Technologies:
Scientific Unit converter is an easy to use unit converter software that allows you to convert between hundreds of units of measurement. It supports 650 units of measurements in 30 different categories. It also comes with a Unit Manager tool to add your own custom units. And a History feature to view your past conversions. A must have tool for all Students, Engineers and Scientists.
It supports the conversion in the following categories - Acceleration, Amt. of Substance, Angle, Area, Base, Computer, Concentration, Fuel Consumption, Density, Distance, Energy, Flow, Force, Light, Power, Watts, Pressure, Sound, Temperature, Time, Torque, Velocity, Volume, Weight, Electric Current, Electricity, Farads, Resistance, and Speed.