A gram is a unit of measure for mass. It is a metric unit and can have certain prefixes that convey units of thousands. For instance, a kilogram is 1,000 grams and a milligram is 1/1000 of a gram. A litre is a metric measure of volume that can also have prefixes. Thus, a millilitre is 1/1000 of a litre. Converting between units of mass and volume requires density, which is mass per unit volume. A common unit of density is grams per millilitre. To convert grams to millilitres, the material should be a liquid.

Write down the mass in grams of a substance. For this exercise, use 50 grams of ethylene glycol (commonly known as antifreeze).

Write down the density of ethylene glycol, which, at 20 degrees C, is 1.1 grams/millilitre.

Divide 50 grams of ethylene glycol by the density of 1.1 grams per millilitre to give 45.45 millilitres of ethylene glycol. This means that approximately 45 millilitres of ethylene glycol weighs 50 grams.