Case 1
- Power output
- 300
- Power unit
- hp (mechanical, 745.7 W)
- Weight
- 1500
- Weight unit
- Kilograms (kg)
149.14W/kg
Open with these valuesPower-to-Weight Ratio Calculator
149.14W/kg
Result: 149.14 W/kgPower divided by the mass it has to move. Watts per kilogram is the SI form and the one cycling uses; motorsport quotes the same quantity as horsepower per tonne. A 300 hp car at 1,500 kg makes 149.14 W/kg, which is 200 hp per tonne. Horsepower here is the mechanical one, 745.6999 W.
Worked examples
Case 2
- Power output
- 250
- Power unit
- W
- Weight
- 70
- Weight unit
- Kilograms (kg)
3.57W/kg
Open with these valuesCase 3
- Power output
- 500
- Power unit
- hp (mechanical, 745.7 W)
- Weight
- 3000
- Weight unit
- Pounds (lb)
274.00W/kg
Open with these valuesHow it's calculated
W/kg = power in watts ÷ weight in kilograms
- StepEnter the power and pick its unit.
- StepEnter the weight the power has to move, and pick its unit.
- StepBoth are converted to watts and kilograms first.
- ResultRead watts per kilogram; the table gives the other two forms.
Reference table
| Power and weight | hp per tonne | hp per lb | W/kg |
|---|---|---|---|
| 250 W and 70 kg | 4.79 | 0.0022 | 3.57 |
| 100 kW and 1200 kg | 111.75 | 0.0507 | 83.33 |
| 300 hp and 1500 kg | 200.00 | 0.0907 | 149.14 |
| 500 hp and 3000 lb | 367.44 | 0.1667 | 274.00 |
Questions
What is power-to-weight ratio?
It is how much power there is for each unit of mass that has to be moved — simply power divided by weight. A higher ratio means quicker acceleration and better climbing, and it predicts performance better than raw power alone.
How do you calculate it?
Divide power by weight in consistent units. Cycling uses watts per kilogram, so 250 W over 70 kg is 3.57 W/kg. Cars are usually quoted as horsepower per tonne, which is the same quantity in different units.
What is a good figure for cycling?
Over about an hour, a recreational rider is often 2 to 3 W/kg, a strong amateur 3.5 to 4.5, and an elite professional 5.5 to 6.5 or more. Because body weight is already in the number, riders of different sizes can compare climbing fairly.
What is a good figure for a car?
A family car sits around 80 to 120 hp per tonne, a hot hatch 150 to 200, a sports car 250 to 350, and a supercar 400 and up. In imperial terms, under about 10 lb per horsepower is genuinely quick.
Which horsepower does this use?
The mechanical horsepower of 745.6999 W, the one the source table lists as 550 ft·lbf/s. The metric Pferdestärke is 735.4988 W and is about 1.4 % smaller, so a figure quoted in PS is not the same number.
Which weight should I enter?
The total mass the power has to move. For a car that is kerb weight, plus the driver if you want a real-world figure; for a cyclist, body weight alone for the classic W/kg, or body plus bike and kit for climbing comparisons.
Sources and last check
Information, not professional advice.