Horsepower, Torque & Power-to-Weight Calculator
Horsepower and torque calculator — convert between horsepower, kilowatts and torque at a given rpm using the exact engine-power relationship, and add vehicle weight to get power-to-weight and a rough 0–100 km/h estimate. Runs in your browser.
Horsepower, Torque & Power-to-Weight Calculator
Enter any consistent combination — e.g. torque + rpm to get power, or hp alone to convert to kW. Add weight for power-to-weight.
How to Use the Horsepower & Torque Calculator
Enter what you know
Type any consistent pair — power and rpm, or torque and rpm, or just horsepower to convert to kW.
Read the conversions
The tool fills in horsepower, kilowatts, torque and rpm instantly.
Add vehicle weight
Enter kerb weight to see power-to-weight in hp/tonne and W/kg.
Gauge acceleration
Read the rough 0–100 km/h estimate — a ballpark from power-to-weight, not a measured figure.
Horsepower, Torque and What Makes a Car Quick
Horsepower and torque are the two numbers every car enthusiast quotes, yet they are constantly confused. Torque is a twisting force — the strength with which the engine turns the crankshaft — while power is the rate at which that force does work, which is why power depends on engine speed as well as force. The relationship between them is exact and simple: power in kilowatts equals torque in newton-metres multiplied by rpm and divided by 9549. This calculator is built on that single equation. Enter any consistent combination — torque and rpm, power and rpm, or just a power figure — and it fills in the rest, converting freely between horsepower and kilowatts (one horsepower being 0.7457 kilowatts) so you can move between the units quoted in different markets.
Understanding the difference matters because the two numbers describe different sensations on the road. Strong low-end torque is what you feel as immediate pull when you press the accelerator, and it is what makes a car good for towing, climbing hills or surging away from low speeds; diesels and electric motors are celebrated for it, with EVs delivering their peak torque from a standstill. Power, by contrast, governs how hard the car keeps pulling at higher revs and ultimately its top speed, which is why high-revving petrol engines feel like they come alive when you extend them. A genuinely satisfying engine balances the two, and seeing how a torque figure at a given rpm translates into power makes that balance concrete. A favourite piece of trivia falls straight out of the maths: in imperial units the power and torque curves always cross at exactly 5252 rpm, purely because of the conversion constant.
What the raw figures cannot tell you on their own is how quick a car will actually feel, and that is where power-to-weight comes in. Acceleration is force divided by mass, so a powerful engine bolted into a heavy body can be no faster than a modest engine in a light one. By entering the vehicle’s weight you get power-to-weight expressed as horsepower per tonne and watts per kilogram — the single best simple predictor of how brisk a car feels — along with a rough 0–100 km/h estimate based on the well-known rule of thumb that the time in seconds is approximately the weight in kilograms divided by the horsepower. That estimate is genuinely handy for a ballpark, but it is only a rule of thumb: it ignores traction, gearing, transmission losses, aerodynamics and how well the car launches, all of which move real-world times around. The conversions, by contrast, are exact, and everything is computed in your browser, so nothing you enter leaves your device.
Torque is the shove you feel; power is how hard it keeps shoving as the revs climb — and power-to-weight is what actually makes a car quick.
10 Facts About Power & Torque
Power = torque × rpm ÷ 9549 (kW, N·m).
1 horsepower = 0.7457 kW; 1 kW ≈ 1.341 hp.
Torque is twisting force; power is torque over time.
Power and torque curves cross at 5252 rpm (in lb-ft/hp units).
Metric horsepower (PS) ≈ 0.9863 hp.
Acceleration depends most on power-to-weight.
A lighter car can out-accelerate a more powerful heavy one.
Diesels make more torque, often at lower rpm.
EV motors deliver peak torque from zero rpm.
This calculator runs in your browser — nothing is uploaded.
Frequently Asked Questions
- Power is the rate of doing work, and for a rotating engine it equals torque multiplied by rotational speed. In metric units, power in kilowatts equals torque in newton-metres times rpm divided by 9549. So torque tells you the twisting force, while power tells you how much of that force is delivered per unit of time — which is why power depends on rpm.
- Multiply horsepower by 0.7457 to get kilowatts, or divide kilowatts by 0.7457 (equivalently multiply by about 1.341) to get horsepower. The calculator does this instantly: enter either value and it fills in the other.
- Yes. Enter any consistent pair and the tool solves the rest. Give it torque and rpm and it returns power in kW and hp; give it power and rpm and it returns the torque; give it just power and it converts between hp and kW. It uses the exact engine-power equation throughout.
- In imperial units (horsepower and pound-feet), the power and torque curves always cross at 5252 rpm, because that is the rpm at which the conversion constant makes the two numerically equal. It is a neat consequence of the units rather than anything physical, and it is a favourite piece of car trivia.
- Because acceleration is force divided by mass. A powerful engine in a heavy car may accelerate no faster than a modest engine in a light one. Power-to-weight — horsepower per tonne, or watts per kilogram — captures this, which is why it is the single best simple predictor of how quick a car feels.
- It uses a well-known rule of thumb: the 0–100 km/h time in seconds is roughly the kerb weight in kilograms divided by the power in horsepower. It is genuinely useful for a ballpark, but it is only a rule of thumb — it ignores traction, gearing, transmission losses, aerodynamics and launch technique, all of which strongly affect real acceleration.
- Torque is what you feel as pulling force — strong low-end torque makes a car feel responsive and good for towing or climbing. Power determines top speed and how hard the car pulls at higher revs. A satisfying car balances both; diesels and EVs are known for abundant low-rpm torque, while high-revving petrol engines make their power higher up.
- PS (Pferdestärke) is the metric horsepower used in much of Europe and Asia, slightly smaller than mechanical horsepower at about 0.9863 hp, or exactly 0.7355 kW. Manufacturers often quote PS, so figures can differ marginally from imperial hp; this tool works in mechanical horsepower and kilowatts.
- Electric motors produce their maximum torque from a standstill, with no need to build revs, so they deliver strong acceleration the instant you press the pedal. Combined with a good power-to-weight ratio, that is why even ordinary EVs can feel brisk away from traffic lights.
- Completely free, with no account or usage limit. It runs entirely in your browser, collects no data, and works offline once the page has loaded.
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