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Power-to-weight ratio (specific power) is a calculation commonly applied to engines and other mobile power plants to enable the comparison of one unit (design) to another. Power-to-weight ratio is a measurement of actual performance of any engine (power plant).

The power-to-weight ratio (Specific Power) formula for an engine (power plant) is:
POWER generated by the engine divided by WEIGHT of the engine as follows:

English system units of measure are usually horsepower per pound (hp/lb)
Metric system units of measure are usually horsepower per kilogram (hp/kg)
The use of watts, or kW (kilowatts), instead of horsepower is common (Conversion: 745.7 watts/hp).

Because this is a ratio, the denominator is always singular (1 lb or 1 kg) as in the following example:
250 hp (engine power)/1,000 lb (engine weight) = 0.25 hp/lb (turbocharged V-8 diesel engine) specific power
70,000 hp (turbine power)/700 lb (turbine weight) = 100 hp/lb (Space Shuttle) specific power
Note: When looking at power to weight ratio (specific power), larger is better.

Weight-to-power ratio (power loading) is a calculation commonly applied to aircraft, cars, and vehicles in general, to enable the comparison of one vehicle performance to another. Weight-to-Power ratio is a measurement of the acceleration capability (potential) of any land vehicle or climb performance of any aircraft or space vehicle).

The Weight-to-Power ratio (power loading) formula for a vehicle is:
weight of the vehicle divided by power generated by the engine as follows:

English system units of measure are usually pounds per horsepower (lb/hp)
Metric system units of measure are usually kilograms per horsepower (kg/hp)
The use of watts, or kW (kilowatts), instead of horsepower is common (Conversion: 745.7 watts/hp).

Because this is a ratio, the denominator is always singular (1 hp or 1 kW) as in the following example:
3,122 lb (automobile weight)/145 hp (V6 (cyl) engine power) = 21.5 lb/hp (2007 Chevy Malibu Is, 5 seats) Power Loading
2,450 lb (aircraft weight)/160 hp (H4 (cyl) engine power) = 15.3 lb/hp (9.25 kg/kW) (Cessna 172 airplane, 4 seats) Power Loading
Note: When looking at weight-to-power ratio (power loading), smaller is better.

• Vehicle metrics

• Weight to Power ratio of current automobiles.