How to use the power to weight ratio calculator
- Enter the power and choose horsepower or kilowatts.
- Enter the weight and choose pounds or kilograms. Use curb weight, or add the driver and fuel for a ready to race figure, and keep the same basis when you compare vehicles.
- Read the result as pounds per horsepower and horsepower per pound, with metric equivalents beside them.
- Run the numbers for a second vehicle to compare them on the same basis.
Formula
Power to weight = power / weight
Pounds per horsepower = weight (lb) / power (hp)
1 hp = 0.745699872 kW and 1 kg = 2.2046226218 lb
Units are converted using exact definitions before dividing, so the pound and kilogram results always agree with each other.
300 hp in a 3,000 lb car
300 hp in 3,000 lb gives 300 / 3,000 = 0.1000 horsepower per pound, which is 10.00 pounds per horsepower or 100 hp per 1,000 lb.
In metric terms, 300 hp is 223.7 kW and 3,000 lb is 1,360.8 kg, so the ratio is 0.1644 kW per kilogram. A metric entry of 150 kW in 1,000 kg gives 0.15 kW per kilogram, or 6.67 kilograms per kilowatt.
What the ratio tells you
Power to weight describes how much weight each unit of power has to move. More power per unit of weight is generally associated with quicker acceleration, all else equal. But all else is rarely equal. Gearing, tires, traction, aerodynamics and how the power is delivered all change real performance, so this ratio is a comparison tool and not a prediction.
Pounds per horsepower and horsepower per pound carry the same information in opposite directions. Both forms are in use, and watts per kilogram is the metric version.
Use the same basis
A fair comparison needs the same kind of weight and the same kind of power for both vehicles. Curb weight with a full tank is common, and so is weight with the driver. Crank horsepower and wheel horsepower are different measurements, and comparing one with the other will mislead.
To turn a ratio into a rough estimate of acceleration, try the quarter mile time estimator. If you have torque and engine speed rather than power, the horsepower from torque calculator comes first.
Assumptions and limits
- Power and weight are positive numbers on a consistent basis.
- The result is a simple ratio, so it does not allow for gearing, grip or drag.
- Unit conversions use exact definitions, rounded only for display.
- Mechanical horsepower is used, not metric horsepower.
Frequently asked questions
How do I calculate power to weight ratio?
Divide the power by the weight. 300 horsepower in 3,000 pounds is 0.1 horsepower per pound, or 10 pounds per horsepower.
Is a lower number of pounds per horsepower better?
A lower number means less weight per unit of power, which generally helps acceleration. It is only one factor, so it cannot decide which vehicle is faster by itself.
What weight should I use?
Pick one basis and use it for every vehicle you compare, such as curb weight or weight with the driver. The tool divides whatever you enter.
Can I mix kilowatts and pounds?
Yes. Choose the unit for each field and the tool converts both before dividing, then shows the result in both unit systems.