Basic arithmetic: + - * / and () for grouping.
Use as to convert units. ex:
4ft * 5ft * 6ft as gallons
Length: Any of mm, cm, m, km, and their full names (millimeter, centimeter, etc.) and purals.
Volume: Any of liter, litre, and their abbreviations.
Length: any of mile, yard, foot, inch: mi, yd, ft, in,
Volume: teaspoon, tablespoon, cup, pint, quart, gallon,