Estimate engine horsepower from quarter-mile time or trap speed, from torque and RPM, or from wheel horsepower.
From torque and RPM: HP = torque (lb·ft) × RPM ÷ 5252. From a quarter-mile run: HP = weight ÷ (ET ÷ 5.825)³. A 3,000 lb car running 12.0 seconds makes about 343 hp.
This calculator gives four ways to estimate an engine's power. Two use a quarter-mile run — the elapsed time (ET) or the trap speed at the finish — together with the vehicle's weight. A third converts torque and engine speed to horsepower. The fourth adds drivetrain loss to wheel horsepower measured on a dyno to estimate crank horsepower.
The quarter-mile formulas are classic drag-racing estimates and assume a well-prepared run; real results vary with traction, gearing, altitude and weather. For the general definition of horsepower and unit conversion, see the Horsepower Calculator.
Each method uses a standard published relationship.
| Input | Estimated power |
|---|---|
| 3,000 lb vehicle, 12.0 s quarter mile | 343.1 hp |
| 1,400 kg vehicle, 14.5 s quarter mile | 200.1 hp |
| 3,000 lb vehicle, 110 mph trap speed | 311.6 hp |
| 300 lb·ft at 5,252 RPM | 300 hp |
| 170 wheel hp with 15% drivetrain loss | 200 hp |
| Drivetrain | Typical loss |
|---|---|
| Manual transmission, front- or rear-wheel drive | 10–15% |
| Automatic transmission | 15–20% |
| All-wheel drive | 20–25% |
Horsepower is torque times angular speed. With torque in lb·ft and speed in RPM, the constants combine to 33,000 ÷ 2π ≈ 5,252. That is why every torque curve crosses the horsepower curve at 5,252 RPM — at that speed, torque and horsepower are numerically equal.
Multiply torque in lb·ft by RPM and divide by 5252. For example 300 lb·ft at 5,252 RPM is exactly 300 hp.
Use HP = weight ÷ (ET ÷ 5.825)³. A 3,000 lb vehicle running 12.0 seconds is about 343 hp.
Trap speed is generally less affected by launch quality, so it often gives a better estimate of power than ET.
The total weight of the vehicle as it ran, including the driver, fuel and any extra load.
Crank (engine) horsepower is measured at the flywheel; wheel horsepower is what reaches the road after drivetrain losses of about 10–25%.
About 15% is a common estimate; automatics and all-wheel drive lose more.
Quarter-mile formulas assume ideal conditions; traction, altitude, temperature, tyres and shift points all change the result.
Multiply by 0.7376. So 400 N·m is about 295 lb·ft.
No — weight, gearing, traction and torque delivery matter too. Power-to-weight ratio is a better guide.
No. Everything runs in your browser.
