Metric Converter is a WP extension for the visual editor that allows to convert metric units to American linear measures (inch, oz, lbs).
WP Unit Converter allows you to convert Length/Distance, Temperature, Time, Weight, Area and Speed metrics in different units of measurement.
This widget can be added anywhere in your site and provides a fully featured unit converter that can be used in various configurations.
Simple to use Unit Converter Plugin. It displays both in Metric and Imperial units.