From Jeff Friesen:
Convert from metres to yards, kilograms to pounds, atmospheres to pascals, or even barleycorns to metres. UC: Units Converter might just be for you. This easy-to-use Windows utility presents a simple GUI with more than 600 common (and not so common) conversions. Although you can freely use Units Converter without payment, you might want to purchase the help manual, which nicely integrates itself into Units Converter. That manual presents a glossary of terms, the multipliers used in the conversions (so you can check out the accuracy of these conversions), and a tutorial that describes this program’s user interface, and error messages.