Calculate hp/lb, lb/hp, hp per ton, and W/kg with power, weight, load, and target-ratio conversions.
Calculator
Power-to-Weight Results
Compare loaded weight, ratio formats, and power needed for the target ratio.
Current and Target Power
Calculation Details
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How to calculate power-to-weight ratio
Enter engine or motor power and the weight it must move. Choose the units independently, and optionally add a driver, passengers, cargo, fuel, or equipment. The calculator converts everything to mechanical horsepower and pounds, then reports the equivalent ratio in common US and metric formats.
power-to-weight ratio = power / loaded weight
weight per horsepower = loaded weight / power
Power-to-weight example
A 300 hp vehicle weighing 3,600 lb has 0.08333 hp/lb, or 12.00 lb/hp. The same ratio is about 166.67 hp per US short ton, 183.72 hp per metric tonne, and 137.00 W/kg. Adding a 180 lb driver changes the loaded weight to 3,780 lb and lowers the ratio to about 0.07937 hp/lb.
Which weight should you enter?
Use the weight that matches the comparison. Curb weight typically includes standard equipment and operating fluids but not occupants or cargo. For a real acceleration or hill-climbing comparison, add the driver and any expected load. Do not compare one vehicle's dry weight with another vehicle's loaded weight.
Crank power versus wheel power
Use the same basis for every vehicle in a comparison. Manufacturer specifications generally report engine or crank power, while a chassis dynamometer reports power delivered at the wheels. Wheel power is normally lower because the drivetrain consumes some power. This calculator does not estimate or add drivetrain loss.
Understanding hp/lb and lb/hp
Higher hp/lb means more power is available for each pound. Lower lb/hp means each horsepower moves less weight. They express the same relationship in opposite directions. A value of 0.10 hp/lb is equivalent to 10 lb/hp and 200 hp per US short ton.
Metric power-to-mass units
Watts per kilogram and kilowatts per metric tonne are numerically identical because one kilowatt is 1,000 watts and one metric tonne is 1,000 kilograms. The calculator uses mechanical horsepower, watts, pounds, and kilograms as defined conversion units. See the NIST Guide to the SI for SI usage and conversion references.
What the ratio can and cannot predict
Power-to-weight ratio is useful for broad comparisons, but it does not directly predict a zero-to-60 time, quarter-mile result, towing performance, or top speed. Traction, gearing, torque curve, aerodynamics, tires, launch control, road grade, temperature, and drivetrain efficiency also matter. Treat the result as one performance input rather than a complete vehicle model.
Target-ratio calculation
The optional target shows how much power the entered loaded weight would need to reach a chosen hp/lb ratio. It also reports the difference from current power. This isolates the power change while holding weight constant; reducing weight can reach the same target by a different path.
Related performance calculators
Use the horsepower calculator to derive power from torque and RPM before comparing ratios. The tire size calculator compares diameter and speedometer effects, and the towing capacity calculator checks vehicle and trailer limits rather than performance ratio.
Frequently asked questions
Should a driver be included?
Include the driver when comparing real operating performance. Leave the optional load at zero when comparing published curb-weight specifications.
Is W/kg the same as kW per tonne?
Yes, the numerical values are the same because both numerator and denominator differ by a factor of 1,000.
Does a higher ratio guarantee faster acceleration?
No. It generally indicates more power relative to mass, but traction, gearing, aerodynamics, and power delivery can change actual performance.