Determine the base unit that is appropriate for your calculation. The metric system uses liters for volume, grams for mass and meters for length.
Weigh or measure your item. Consider using a prefix if the item is more than 10 or less than one of the base units. If you are weighing your object and it weighs 2000 grams, for example, you should use a prefix to make it simpler.
Choose a prefix to use. Each prefix corresponds with 10 of the previous prefix or base unit. Your item that weights 2000 grams would be converted to two kilograms, as a kilogram equals 1000 grams.