Liquid propane (LP) is frequently sold in gallons but burned as cubic meters. This presents a confusing calculation for many who are trying to calculate the burning time for their home or RV heaters. If you are traveling to a country that uses the metric system, such as Canada, and are filling your camping trailer or RV LP tanks, there is a formula to use to convert an LP gallon measurement to cubic meters.
Things You'll Need
 Calculator
 Pen and paper

Determine your tank size in gallons. It may be printed on the tank. If not, fill the tank completely and then note the reading on the tank gauge.

Multiply the gallon measurement by 0.81756 to obtain cubic millimeters. For example, if there are 20 gallons in the tank, 20 times 0.81756 equals 16.3512 cubic millimeters. There are 1,000 cubic millimeters in a cubic meter.

To obtain cubic meters, divide your first result by 1,000. In our example, 16.3512 divided by 1,000 equals 0.0163512, or 0.0164 (rounded up) cubic meters.
References
 Photo Credit Propane Tank image by John Walsh from Fotolia.com