Convert Units Free HD is a unit converter for iPad which supports 13 units i.e. Angle, Area, Data, Energy, Force, Length, Mass, Power, Pressure, Speed, Temperature, Time, Volume and lets you create custom formula with basic multiplier support.
The units are displayed on circular dials on both sides which can be rotated to change. To create a custom formula touch the blue circular button and scroll down to select Custom and then create one. You can name the units and set a conversion factor to convert both.
Because all the units are on circular panel, you can switch between them very fast and see how one convert into rest of them. I found this feature particularly very useful as it helps you to compare.
Download Convert Units Free HD for iPad