What is the power to weight ratio?
Type the power and the weight of a car, motorcycle, bike or rider to get the power to weight ratio. The power to weight ratio calculator gives it in watts per kilogram, horsepower per pound and per ton, and as pounds per horsepower. Or type a ratio and one of the others to find the power or the weight.
- Power to weight ratio (W/kg)
- 140.91
The power to weight ratio is 140.91 W/kg, or 11.667 lb per hp.
- hp per ton
- 171.43
- hp per lb
- 0.085714
- Weight to power (lb per hp)
- 11.667
- Weight to power (kg per kW)
- 7.0966
Power to weight ratio (W/kg): 140.91. The power to weight ratio is 140.91 W/kg, or 11.667 lb per hp.
How to calculate
Finds the power-to-weight ratio of a car, motorcycle, bike or rider from power and weight, in W/kg, hp per lb, hp per ton and lb per hp, or the power or weight from the ratio.
Example with the default inputs (Power 300 hp, Weight 3,500 lb): The power to weight ratio is 140.91 W/kg, or 11.667 lb per hp.
Formula: ratio = power ÷ mass in W/kg; power = ratio × mass; mass = power ÷ ratio. 1 hp = 550 ft·lbf/s = 745.69987 W, 1 lb = 0.45359237 kg, 1 short ton = 2,000 lb.
- Weight means mass: the ratio divides power by mass, as is usual for cars, bikes and cyclists.
- Horsepower (hp) is mechanical horsepower, 550 ft·lbf/s; metric horsepower (PS) is 75 kgf·m/s = 735.49875 W.
- Values run in watts and kilograms, in double precision.
Worked examples
Each example is checked against the calculator on every build.
- Power 134.1 hp, Weight 2,205 lb gives Power to weight ratio (W/kg) 100, Weight to power (kg per kW) 10, hp per lb 0.060828, Weight to power (lb per hp) 16.439868.Source: OpenStax, University Physics Volume 1, §7.4 Power (power is the rate of doing work, in watts), https://openstax.org/books/university-physics-volume-1/pages/7-4-power (retrieved 2026-10-02); NIST Special Publication 811, Appendix B (1 hp = 550 ft·lbf/s = 745.699 872 W; 1 lb = 0.453 592 37 kg), https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-02)
- Power 300 hp, Weight 3,500 lb gives Weight to power (lb per hp) 11.666667, hp per ton 171.428571, Power to weight ratio (W/kg) 140.913155.Source: NIST Special Publication 811, Appendix B (1 hp = 550 ft·lbf/s = 745.699 872 W; 1 lb = 0.453 592 37 kg), https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-02)
- Power to weight ratio (W/kg) 4, Weight 154.3 lb gives Power 0.3755 hp.Source: OpenStax, University Physics Volume 1, §7.4 Power (power is the rate of doing work, in watts), https://openstax.org/books/university-physics-volume-1/pages/7-4-power (retrieved 2026-10-02)
How it works
For a power P and a weight (mass) m:
- ratio = P ÷ m, in watts per kilogram (W/kg), with P in watts and m in kilograms
- power P = ratio × m; weight m = P ÷ ratio
- hp per lb = ratio × 0.45359237 ÷ 745.6998715822702
- hp per ton (US short ton of 2,000 lb) = hp per lb × 2,000
- lb per hp = 1 ÷ (hp per lb); kg per kW = 1,000 ÷ ratio
Type any two of power, weight and ratio. Powers are converted to watts (1 hp = 550 ft·lbf/s = 550 × 0.3048 × 9.80665 × 0.45359237 W = 745.6998715822702 W; 1 PS = 75 × 9.80665 W = 735.49875 W; 1 kW = 1,000 W) and weights to kilograms (1 lb = 0.45359237 kg; 1 short ton = 2,000 lb; 1 t = 1,000 kg). The maths runs in double precision.
Rules
- Power, weight and ratio are each more than 0. Power is at most 10¹² W, weight at most 10⁶ kg, and the ratio at most 10⁶ W/kg; a solved value outside these bounds has no answer.
- Weight is used as mass, as in car and cycling specifications.
Output format. Every ratio to 5 significant figures.
Worked examples by hand
A 100 kW car of 1,000 kg. ratio = 100,000 ÷ 1,000 = 100 W/kg; kg per kW = 1,000 ÷ 100 = 10; hp per lb = 100 × 0.45359237 ÷ 745.69987 = 0.060828; lb per hp = 16.44.
A 300 hp car of 3,500 lb. lb per hp = 3,500 ÷ 300 = 11.667; hp per ton = 300 ÷ (3,500 ÷ 2,000) = 171.43; ratio = 300 × 745.69987 W ÷ (3,500 × 0.45359237 kg) = 140.91 W/kg.
A 70 kg cyclist at 4 W/kg. power = 4 × 70 = 280 W.
Other questions people ask
How do I calculate the power to weight ratio?
Divide the power by the weight (mass): ratio = power ÷ weight. A 100 kW car that weighs 1,000 kg has 100,000 W ÷ 1,000 kg = 100 W/kg.
What is the power to weight ratio of a 300 hp, 3,500 lb car?
300 hp ÷ 3,500 lb = 0.0857 hp per lb, or 171.4 hp per ton (3,500 lb is 1.75 short tons). Turned the other way, 3,500 ÷ 300 = 11.67 lb per hp. In metric units it is 140.9 W/kg.
Is a higher or lower number better?
A higher power to weight ratio (more W/kg or hp per ton) means more power for each unit of weight, so quicker acceleration and climbing, other things equal. For the inverse, weight to power (lb per hp), lower is quicker.
How is W/kg used in cycling?
Cyclists divide the power they can hold, in watts, by their body weight in kilograms. A 70 kg rider who holds 280 W rides at 4 W/kg. Type 4 as the ratio and 70 kg as the weight to get 280 W.
Which horsepower does the page use?
Horsepower (hp) is mechanical horsepower: 550 foot-pounds per second, or 745.69987 W (NIST SP 811). OpenStax rounds it to 746 W. Metric horsepower (PS) is 735.49875 W and can be picked as the power unit.
Should I include the driver?
Either way works if you compare like with like. Makers often quote curb weight without a driver; adding the driver gives a ratio closer to what you feel on the road.