Gas measure is a term used to describe the units of measurement used to quantify the amount of gas present in a given area. The two most common units of measurement for gas are the therm and the gallon. A therm is a unit of energy equal to 100, 000 British thermal units (BTUs) and is typically used to measure natural gas. A gallon is a unit of volume equal to 128 fluid ounces and is commonly used to measure liquid fuels such as gasoline.