Learn & Understand

Comparing Apples to Cubic Feet: The Gasoline Gallon Equivalent

How do you compare a car that runs on cubic feet of compressed gas with one that runs on gallons of gasoline? The fuels are measured in entirely different units, making direct comparison meaningless. The clever solution — the gasoline gallon equivalent — lets wildly different fuels be weighed on a single, fair scale of energy.

Different Fuels, Different Units

Fuels come measured in incompatible ways: liquid fuels by the gallon or liter, gaseous fuels by the cubic foot or cubic meter, others by weight. A driver comparing a gasoline car with one running on compressed natural gas or hydrogen faces a puzzle — the numbers simply do not line up. Volume, mass, and energy are being counted in different currencies.

The Common Denominator: Energy

The way through is to convert everything to energy, the one thing all fuels ultimately provide. A fuel's value lies in the energy it delivers, so comparing fuels by their energy content puts them on equal footing. This is the principle behind equivalence units: express each fuel in terms of how much of a familiar fuel would hold the same energy.

The Gasoline Gallon Equivalent

For compressed natural gas, the standard is the gasoline gallon equivalent — the amount of gas containing the same energy as one gallon of gasoline. By pricing and rating gas fuel in these equivalents, a driver can compare a gas vehicle's efficiency and cost directly against a gasoline car, as though both ran on the same fuel. The equivalence unit translates cubic feet into familiar terms.

Fair Comparison Across Fuels

Equivalence units matter increasingly as vehicles run on ever more varied fuels — gasoline, gas, electricity, hydrogen. Reducing them all to a common energy basis is the only honest way to compare their efficiency and cost per mile. Behind the tidy “equivalent” figure lies the simple, powerful idea that what really counts is the energy a fuel delivers.

Estimating CNG Use

To convert distance into gas volume, use the CNG Consumption Calculator. Compare with piped gas via the Natural Gas Consumption Calculator, and cost per mile via the Fuel Cost Per Mile Calculator.