Units
Units is a plugin that can convert between any units of measure, and comes with a Field for content authors to use.
You can convert from meters to feet, or liters to gallons, and anything else in between.
It also has helper functions to output values as fractions, get the parts of a value, and a whole lot more.
Free
Package Name
To install this plugin, search for its package name on the Plugin Store and click “Install”.