Engine Horsepower Calculator
Estimate engine power in HP, kW and PS from torque and RPM, using metric (N·m) or imperial (lb-ft) formulas.
Metric: kW = torque (N·m) × RPM ÷ 9549. Imperial: HP = torque (lb-ft) × RPM ÷ 5252.
Power output
85 HP
Power output
62.83 kW
1 HP ≈ 0.7457 kW
This is a theoretical figure from torque and speed; real wheel output is lower due to drivetrain losses.
Last updated: January 2026
How this calculator is verified
Checked by True Calculator automated test suite on
- Formula verified against a published worked example in the automated test suite
- Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests
The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.
When to Use This Calculator
Use this calculator when comparing engines across specifications that quote different units — a scooter rated in bhp, a car brochure quoting kW, and a truck spec in PS all need a common scale. Before a purchase, check whether the claimed power is plausible from the torque curve, or estimate the power of a modified engine after a bore, cam or turbo change. Mechanics use the relation to sanity-check dyno readings, and students use it to connect physics concepts to real vehicles. It also helps when importing data from overseas sources that quote lb-ft and imperial horsepower, so every engine lands on the same kW and HP numbers before you compare them.
How to Use This Calculator
- Step 1: Find the engine's peak torque figure from the owner's manual or a dyno sheet.
- Step 2: Choose metric (N·m) or imperial (lb-ft) to match the unit your figure uses.
- Step 3: Enter the RPM at which that torque is produced.
- Step 4: Read the power in kW and HP, then compare against the manufacturer's claimed figure.
Worked Example
A car's engine produces 200 N·m of torque at 3000 RPM. Select metric and enter 200 and 3000. The calculator uses kW = 200 × 3000 ÷ 9549, giving 62.83 kW, and converts that to 85.43 HP. If the same engine were rated in imperial units at 300 lb-ft and 4000 RPM, it would show 228.48 HP. Crank figures like these are always a little higher than what reaches the wheels.
Tips and Common Mistakes
- •Use the torque at the RPM where it peaks — using redline RPM with peak torque overstates power.
- •Two-wheelers in India are usually rated in bhp; this tool's HP figure is directly comparable.
- •For quick comparisons, 1 kW is roughly 1.36 HP, so a 100 kW engine is about 136 HP.
- ✗Avoid mixing units — entering N·m with the imperial formula gives a meaningless result.
- ✗Don't treat crank power as wheel power; expect 10–20% drivetrain loss on cars.
Frequently Asked Questions
How is horsepower calculated from torque?
Power is torque times rotational speed. In metric units, kW = torque (N·m) × RPM ÷ 9549; in imperial units, HP = torque (lb-ft) × RPM ÷ 5252. A 200 N·m engine at 3000 RPM produces about 62.83 kW, or 85.43 HP.
What is the difference between metric and imperial horsepower?
Metric power is expressed in kilowatts (1 kW = 1.35962 HP), while imperial horsepower is the lb-ft × RPM ÷ 5252 figure used in the US. The two scales differ by about 1.4%.
Why does power change with RPM?
Horsepower grows roughly in proportion to RPM until torque starts falling off. That is why engines show a peak-power RPM, usually well before the redline, and why this calculator needs RPM as an input.
Is calculated power the same as what reaches the wheels?
No. Crank figures from this formula are always higher than wheel figures because of losses in the gearbox, differential and tyres — typically 10–20% for a car, less for a two-wheeler.
Can I use this for electric motors?
Yes — the same torque and speed relation holds. For electric motors, input power is usually given in kW and this calculator converts it directly to horsepower for comparison.
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