mathjs/docs/units.md

Unit

Math.js supports units. Basic operations add, subtract, multiply, and divide can be performed on units. Trigonometric functions like sin support units with an angle as argument. Units can be converted from one to another using function in, an the value of a unit can be retrieved using toNumber.

var a = math.unit(55, 'cm');    // 550 mm
var b = math.unit('0.1m');      // 100 mm
math.add(a, b);                 // 0.65 m
b.in('cm');                     // 10 cm  Alternatively: math.in(b, 'cm')
b.toNumber('cm');               // 10

math.eval('2 inch in cm');      // 5.08 cm
math.eval('cos(45 deg)');       // 0.7071067811865476