Horsepower Calculator
Calculate horsepower from torque and RPM, or estimate it from quarter-mile times.
Please note: An estimate based on the figures you entered. Real-world results vary with conditions this calculation cannot see, so treat it as a starting point rather than a final answer.
What the Horsepower Calculator does
Power is the rate of doing work, so it combines how hard an engine twists with how fast it spins. The trap-speed and elapsed-time formulas invert that relationship empirically, estimating power from how quickly a known mass was accelerated over a quarter mile.
Formula
hp = Torque (lb·ft) × RPM ÷ 5252kW = Torque (N·m) × RPM ÷ 9549hp = Weight × (Trap speed ÷ 234)³hp = Weight ÷ (ET ÷ 5.825)³
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Calculate from | one of 3 options | Yes | — |
| Torque | number | In some modes | Accepts more than 0. Shown Calculate from is Torque and engine speed. |
| Torque unit | one of 2 options | In some modes | Shown Calculate from is Torque and engine speed. |
| Engine speed | rpm | In some modes | Accepts more than 0. Shown Calculate from is Torque and engine speed. |
| Vehicle weight | number | In some modes | Accepts more than 0. Shown Calculate from is Quarter-mile trap speed, or Calculate from is Quarter-mile elapsed time. |
| Trap speed | mph | In some modes | Accepts more than 0. Shown Calculate from is Quarter-mile trap speed. |
| Elapsed time | seconds | In some modes | Accepts more than 0. Shown Calculate from is Quarter-mile elapsed time. |
| Vehicle weight for power-to-weight | number | Optional | Accepts 0 or more. Shown Calculate from is Torque and engine speed. |
| Weight unit | one of 2 options | Yes | — |
How to use it
- Choose Calculate from and Weight unit.
- Fill in the remaining inputs the form shows for your choice.
- Select Calculate.
Worked example
An engine producing 300 lb·ft at 5,000 rpm.
- Torque
- 300 lb·ft
- RPM
- 5,000
300 × 5,000 ÷ 5,252 = 285.6 hp, which is 213.0 kW or 289.5 PS.
Frequently asked questions
Why do horsepower and torque curves always cross at 5,252 rpm?
Because hp = torque × rpm ÷ 5252. When rpm equals 5,252 the multiplier is exactly 1, so the two curves must meet there regardless of the engine.
Is torque or horsepower more important?
Torque is what you feel; horsepower is what determines how quickly you can keep accelerating. Power is torque sustained at speed, which is why gearing matters so much.