From Savard Software:
Master Converter is a powerful Microsoft Windows utility that can quickly and easily convert to and from over 600 different units in 33 categories. The categories include: length, area, volume, dry volume, time, speed, mass, density, force, pressure, energy, power, flow, temperature, angle, luminance, illumination, numbers, fractions, data transfer, data storage, radiation, and more. The ability to add your own custom units and categories ensures that Master Converter will grow with your needs. Master Converter's intuitive and powerful interface makes it extremely easy to convert values from a wide range of units in several categories.