Calculate horsepower, weight, or trap speed from two known values using drag strip speed formulas in hp, lbs, mph, kW, kg, or kph.
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Horsepower Trap Speed Formula
The horsepower trap speed calculator uses the common quarter-mile trap speed estimate. It works with horsepower, vehicle weight, and trap speed. Enter any two values to solve for the third.
HP = W * (V/234)^3
W = HP / (V/234)^3
V = 234 * cbrt(HP/W)
- HP = horsepower
- W = vehicle weight in pounds
- V = trap speed in miles per hour
- 234 = quarter-mile trap speed constant used in this estimate
- cbrt = cube root
If you leave horsepower blank, the calculator estimates horsepower from weight and trap speed. If you leave weight blank, it estimates the vehicle weight that matches the horsepower and trap speed. If you leave trap speed blank, it estimates the quarter-mile trap speed from horsepower and weight.
The calculator converts kW to horsepower, kg to pounds, and kph to mph before applying the formula, then converts the result back to your selected unit.
Trap Speed Estimates by Power-to-Weight Ratio
These values show approximate quarter-mile trap speeds from the formula. Use total race weight, including the driver and fuel, for the closest comparison.
| Horsepower / Weight | Example | Estimated Trap Speed |
|---|---|---|
| 0.08 hp/lb | 280 hp at 3,500 lb | 100.7 mph |
| 0.10 hp/lb | 350 hp at 3,500 lb | 108.6 mph |
| 0.12 hp/lb | 420 hp at 3,500 lb | 115.4 mph |
| 0.15 hp/lb | 525 hp at 3,500 lb | 124.2 mph |
| 0.20 hp/lb | 700 hp at 3,500 lb | 136.8 mph |
Horsepower Trap Speed Examples
Example 1: Calculate trap speed
You have 450 hp and a race weight of 3,500 lb.
V = 234 * cbrt(450/3500)
V = 118.1 mph
The estimated trap speed is 118.1 mph.
Example 2: Calculate horsepower
You know the car weighs 3,600 lb and traps 120 mph.
HP = 3600 * (120/234)^3
HP = 486.2 hp
The estimated horsepower is 486.2 hp.
Horsepower Trap Speed FAQ
Should you use curb weight or race weight?
Use race weight. That means the vehicle, driver, fuel, and anything else in the car during the pass. Trap speed is affected by the total weight being accelerated, so curb weight alone can make the horsepower estimate too low.
Is this wheel horsepower or engine horsepower?
The formula estimates horsepower based on observed performance, but the meaning depends on the data you compare it to. If you use actual track trap speed and race weight, the result is often treated as an approximate effective horsepower number. It may be closer to wheel horsepower than rated crank horsepower because drivetrain loss is already reflected in the car’s performance.
Why does trap speed give a better horsepower estimate than elapsed time?
Trap speed is less affected by launch, traction, gearing, and driver reaction than elapsed time. A poor launch can hurt elapsed time badly while still producing a strong trap speed. That is why trap speed is commonly used for quick horsepower estimates.