Lets you convert between a TON of different units. Requires a free sign-up.

<a href="http://www.tappingware.com/unitconverter/UnitConverter.php" title="Unit Converter for iPhone" target="_blank"><img src="http://www.modmyi.com/images/apps/unitconverter.png" border="0" height="353" width="319" /></a>

<a href="http://www.tappingware.com/unitconverter/UnitConverter.php" title="Unit Converter for iPhone" target="_blank">http://www.tappingware.com/unitconverter/UnitConverter.php</a>