iUnit

iUnit is a unit conversion program for the Macintosh. You can convert between 550 different units quickly and easily. iUnit also displays the values of 42 physical constants.

Constants: 
Mathematical 
Physical 
Planets 

Units: 
Acceleration
Angle
Area
Capacitance
Concentration
Corrosion Rate
Currency
Currency - European Union
Density
Diffusitivity
Distance
Electrical Conductance
Electrical Charge
Energy
Enthalpy - mol basis
Enthalpy - mass basis
Enthalpy - volume basis
Entropy
Force
Heat Capacity
Heat Flux
Heat Rate
Heat Transfer Coefficient
Industrial Weight Per Area Units
Luminous Luminence
Luminous Intensity
Magnetic Flux
Magnetic Flux Density
Magnetic Field Strength
Mass
Momentum
Moment-Torque
Power
Pressure
Radiation Activity
Stress
Surface Tension
Temperature
Thermal Conductivity
Thermal expansion - linear
Thermal expansion - volume
Time
Type (printer's)
Velocity
Volume
Volume Flow Rate