From URVAS Engineering:
Unit Converter for Excel is an addin for the Microsoft Excel to perform various conversions between many types of measurement units. The units are grouped in the following categories: Dimensions and capacity, Energy and power, Mechanics, Hydraulics, Heat, Electricity, Magnetism, Light and sound, Radiation.
You can also use UNITCONV, DECIMALFEET and FRACTIONALFEET functions to perform conversions.
Unit Converter for Excel works under Windows 95, Windows 98, WinMe, Windows NT 4.0, Windows 2000, Windows XP, Windows Vista, Windows 7 with Microsoft Excel 2000, XP, 2003, 2007 or 2010 installed.