Power-to-Weight Ratio Calculator (kW/t, hp/t, kg per PS, lb per hp)

Understanding the power-to-weight ratio calculator — concept and principle

This calculator works out a vehicle's power-to-weight ratio in kW per tonne, horsepower per tonne and metric horsepower per tonne, and the inverse, weight per horsepower. Car enthusiasts and riders use it to compare cars, motorcycles and bikes of different sizes on equal terms.

Power per tonne: with the default inputs the result is 107.1 kW/t (6.86 kg per PS).

How it is calculated

Power is converted to watts: 1 kW = 1,000 W, 1 hp = 745.69987 W, 1 PS = 735.49875 W.
Weight is converted to kg (lb × 0.45359237).
kW per tonne = watts ÷ kg (W/kg equals kW/t).
hp per tonne and PS per tonne = power in that unit ÷ (kg ÷ 1,000).
Weight per power: kg/PS = kg ÷ PS; lb/hp = lb ÷ hp.

The principle

Acceleration is force divided by mass, and the power available sets how much force the engine can deliver at a given speed. Dividing power by mass therefore gives a rough measure of how quickly a vehicle can gain speed. A light car with modest power can match a heavy car with much more power. The inverse figure, weight per horsepower, is popular in Korea and Japan (kg/PS) and the US (lb/hp); lower is quicker. Gearing, traction, aerodynamics and the shape of the power curve also matter, so the ratio is a comparison, not a precise prediction.

Worked example

Default inputs: 150 kW, 1,400 kg.

Power-to-weight = 150,000 W ÷ 1,400 kg = 107.1 kW/t.
hp = 150,000 ÷ 745.7 = 201.2; per tonne = 201.2 ÷ 1.4 = 143.7 hp/t.
PS = 150,000 ÷ 735.5 = 203.9; per tonne = 145.7 PS/t; kg/PS = 1,400 ÷ 203.9 = 6.86.
lb/hp = 3,086.5 ÷ 201.2 = 15.34.

Each point is the calculator re-run with only “Vehicle weight” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Vehicle weight	Power-to-weight (kW per tonne)
350	428.6
700	214.3
1,050	142.9
1,400	107.1
1,750	85.7
2,100	71.4
2,800	53.6

How to read the result

Compare vehicles using the same unit and the same definition of weight (kerb weight versus with a driver). A higher kW/t or a lower kg/PS means quicker acceleration potential. Including the driver's weight makes a noticeable difference for light vehicles such as motorcycles.

Common mistakes

Mixing mechanical hp and metric PS, which differ by about 1.4%.
Comparing kerb weight with gross weight.
Treating the ratio as a 0–100 km/h time.
Using peak power when the vehicle rarely reaches it.

Keep in mind: The ratio is a comparison tool only. Drive within the law and the conditions.

Frequently asked questions

What is a good power-to-weight ratio?

Higher means quicker; compare cars of the same class using the same weight definition.

What is the difference between hp and PS?

1 hp is 745.7 W and 1 PS is 735.5 W; PS is the metric horsepower.

How do I convert kW/t to kg/PS?

Divide 1,000 by (kW/t × 1.36), since 1 kW ≈ 1.36 PS.

Sources: NIST Special Publication 811 (2008), Appendix B (horsepower, metric horsepower and pound definitions)

Checked 9 Nov 2026. Unit definitions: 1 mechanical horsepower = 550 ft·lbf/s = 745.69987 W; 1 metric horsepower (PS) = 75 kgf·m/s = 735.49875 W; 1 lb = 0.45359237 kg (standard values).

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