Automotive
Estimate engine horsepower from quarter-mile trap speed or elapsed time performance.
Estimated Horsepower
332hp
Based on trap speed (fox) performance
This calculator uses standard quarter-mile performance formulas. Results are estimates; actual horsepower may vary based on transmission type, conditions, and drivetrain losses.
An engine horsepower calculator estimates your engine's output based on quarter-mile performance metrics. Input your vehicle weight and either trap speed (mph) or elapsed time (seconds) from a quarter-mile run, and the calculator applies industry-standard formulas to derive horsepower and power-to-weight ratio.
The calculator uses two established formulas: the Fox method (HP = Weight × (Trap Speed / 234)³) for trap speed, and the elapsed-time method (HP = Weight / (ET / 5.825)³) for quarter-mile time. Both account for vehicle weight to normalize performance. The result includes estimated horsepower, power-to-weight ratio, and the method used.
Trap Speed: HP = Weight × (Trap Speed / 234)³ | Elapsed Time: HP = Weight / (ET / 5.825)³The Fox formula uses trap speed in mph and vehicle weight in lbs to estimate horsepower. The elapsed-time (ET) formula uses quarter-mile time in seconds. Both are empirical formulas derived from extensive drag racing data. Power-to-weight ratio (hp/lb) is calculated by dividing estimated horsepower by vehicle weight.
| Input | Result | Notes |
|---|---|---|
| Weight: 3200 lbs | Trap Speed: 110 mph | Horsepower: 343 hp | Power-to-Weight: 0.11 hp/lb | Typical modern V8 sedan with solid acceleration and trap speed |
| Weight: 2800 lbs | Elapsed Time: 12.0 seconds | Horsepower: 283 hp | Power-to-Weight: 0.10 hp/lb | Lightweight sports car with quick quarter-mile performance |
| Weight: 4200 lbs | Trap Speed: 115 mph | Horsepower: 552 hp | Power-to-Weight: 0.13 hp/lb | High-performance SUV or muscle car with strong trap speed despite weight |
Trap speed is the maximum speed measured during the last 66 feet of a quarter-mile run. Elapsed time is the total time to complete a quarter-mile. Both correlate to horsepower but use different formulas. Trap speed is generally more consistent for estimation.
Yes—use the total weight of the vehicle as tested, including driver, passengers, fuel, and cargo. This is your actual weight during the quarter-mile run and affects the horsepower calculation.
Quarter-mile formulas estimate crank horsepower from track performance. Actual engine output varies due to drivetrain losses, traction conditions, atmospheric pressure, fuel quality, and engine tuning. Dyno results are direct measurements and may differ by 5–20%.
0.08–0.10 hp/lb is typical for daily drivers; 0.10–0.13 is sporty; 0.13–0.15 is performance-oriented; above 0.15 is high-performance. Supercars often exceed 0.20 hp/lb.
Yes—enter the motorcycle's weight (including rider) and its quarter-mile trap speed or ET. The formulas work for any vehicle. Motorcycles often have excellent power-to-weight ratios due to low mass.
No—these are baseline formulas for naturally aspirated engines. Turbocharged, supercharged, or nitrous-assisted vehicles may see different relationships between trap speed and actual horsepower due to non-linear power delivery.