propellant efficiency

For stationary and shaft engines including propeller engines, fuel consumption is measured by calculating the brake specific fuel consumption which measures the number of pounds of fuel that is needed to generate an hours' worth of horsepower-energy. In metric units, the number of grams of fuel needed to generate a kilowatt-hour of energy is calculated.

For internal combustion engines in the form of jet engines, the power output varies drastically with airspeed and a less variable measure is used: thrust specific fuel consumption (TSFC), which is the number of pounds of propellant that is needed to generate impulses that measure a pound an hour. In metric units, the number of grams of propellant needed to generate an impulse that measures one kilonewton per second.

For rockets— TSFC can be used, but typically other equivalent measures are traditionally used, such as specific impulse and effective exhaust velocity.