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Power-to-Weight Calculator

Work out a car's power-to-weight ratio in hp and kW per tonne, and its weight per horsepower in kg and lb. Enter power in hp or kW and weight in kg or lb.

horsepower

Peak engine power. hp is mechanical horsepower.

kilograms

Use the same basis when comparing cars, e.g. kerb weight.

Results

Power-to-weight ratio

200 hp/tonne

Per metric tonne (1,000 kg). Higher means more power for each kilogram.

Ratio in kW/tonne
149.14 kW/tonne
Weight per hp (kg)
5 kg/hp
Weight per hp (lb)
11.02 lb/hp

200 horsepower per tonne, 149.14 kilowatts per tonne. 5 kilograms or 11.02 pounds per horsepower.

Formula

hp per tonne
= power (hp) ÷ weight (kg) × 1,000
kW per tonne
= power (kW) ÷ weight (kg) × 1,000
kg per hp
= weight (kg) ÷ power (hp)
lb per hp
= weight (lb) ÷ power (hp)

A tonne is the metric tonne of 1,000 kg. 1 hp (mechanical horsepower) is 0.7457 kW and 1 lb is 0.45359237 kg; the calculator converts whichever units you enter.

Worked example

A car has 300 hp and weighs 1,500 kg.

  1. Step 1: hp per tonne

    300 ÷ 1.5 = 200 hp/tonne

  2. Step 2: Power in kW

    300 × 0.7457 = 223.71 kW

  3. Step 3: kW per tonne

    223.71 ÷ 1.5 = 149.14 kW/tonne

  4. Step 4: kg per hp

    1,500 ÷ 300 = 5 kg/hp

  5. Step 5: lb per hp

    3,306.93 ÷ 300 = 11.02 lb/hp

The car has 200 hp per tonne (149.14 kW per tonne), so each horsepower moves 5 kg, or 11.02 lb.

Use the same weight for every car you compare

Manufacturers quote weight on different bases: some figures are for an empty car, others include fluids, a full or partly full tank, or an allowance for the driver. A difference in basis can change the ratio as much as a real difference between cars, so compare figures measured the same way, or add your own weight with a driver and passengers if that is what you want to know.

Horsepower, kW and PS

The calculator's hp is mechanical horsepower, 745.7 W, which is what "hp" and "bhp" mean in the US and UK. Many European figures are in PS (metric horsepower, exactly 735.49875 W), which is about 1.4% smaller: multiply PS by 0.9863 to get hp, or enter the kW figure instead.

kW per tonne is numerically the same as watts per kilogram.

What power-to-weight does not tell you

Power-to-weight is a useful way to compare how much performance potential two vehicles have, but it is only one factor. It does not predict a 0–60 mph time, a quarter-mile time or a top speed, because these also depend on:

  • traction and how the power reaches the road;
  • gearing and the transmission;
  • how power and torque vary across the rev range, not just the peak figure;
  • aerodynamic drag, which dominates at high speed;
  • tires, launch technique, weather and the driver.

Frequently asked questions

How do I calculate power-to-weight ratio?

Divide the power by the weight in tonnes (kg ÷ 1,000). A 300 hp car weighing 1,500 kg has 300 ÷ 1.5 = 200 hp per tonne.

How do I get hp per ton instead of per tonne?

A US (short) ton of 2,000 lb is 0.907185 tonnes, so multiply hp per tonne by 0.907185 to get hp per US ton. The calculator uses the metric tonne of 1,000 kg.

What is a good power-to-weight ratio?

It depends on what you are comparing. The ratio is most useful for comparing two vehicles measured the same way; a higher number means more power for each kilogram, but it does not on its own tell you how fast a car will accelerate.

Can I enter PS or bhp?

bhp is mechanical horsepower, so enter it as hp. For PS, either enter the kW figure or multiply PS by 0.9863 to convert it to hp first.

Is weight per horsepower the same thing?

It is the same comparison turned upside down: kg or lb per hp tells you how much weight each horsepower has to move, so lower is better. Both are shown.

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