One liter equals 1,000 grams, so 250 grams is the equivalent to 0.25 liters. A liter is a measure of volume, and 1 cubic meter is the equivalent of 1,000 liters or 1,000,000 grams.
Since grams and liters are both metric units of measurement, they have a base of 10, which means that converting grams to liters simply requires a person to divide 1,000 by the amount of grams. A person could also just move the decimal point three places to the left. Likewise, converting liters to grams involves multiplying by 1,000 or moving the decimal point three places to the right.