Convert between common units of length, weight, temperature, and volume.
Length: millimeters, centimeters, meters, kilometers, inches, feet, yards, miles.
Weight: milligrams, grams, kilograms, ounces, pounds, stone, metric tons.
Temperature: Celsius, Fahrenheit, Kelvin.
Volume: milliliters, liters, cups, pints, quarts, gallons (US), fluid ounces.