# Horsepower Calculator (Quarter Mile)

URL: https://speedycalculator.com/calculators/everyday-life/quarter-mile-horsepower/
Last updated: 2026-10-25

> The quarter-mile horsepower calculator estimates engine horsepower from a car's weight and its quarter-mile elapsed time (ET) or trap speed, using the well-known drag-racing formulas.

## Inputs

- Race weight (car + driver) (lb, kg, g, oz)
- Quarter-mile elapsed time (s)
- Trap speed (mph, km/h, m/s, knots)

## Results

- Horsepower from elapsed time
- Horsepower from trap speed
- Trap-speed power in kW

## Formula

```
From elapsed time: hp = weight (lb) ÷ (ET ÷ 5.825)³
From trap speed: hp = weight (lb) × (trap speed mph ÷ 234)³
```

## Explanation

Drag racers have long estimated power from time slips. The trap-speed formula is usually more reliable because it depends less on the launch and traction; the elapsed-time formula is sensitive to wheelspin and reaction at the start. Both estimate power at the wheels converted back to an approximate flywheel figure.

### How to use the Horsepower Calculator

- **Race weight (car + driver)**
- **Quarter-mile elapsed time**
- **Trap speed**
- Every result field is editable: type into **Horsepower from elapsed time** and **Quarter-mile elapsed time** plus every other field update to match.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the race weight of the car with driver, then the quarter-mile elapsed time and/or the trap speed.

### Tips

- Use your own measured figures – fuel economy, speed and prices vary a lot with driving style, traffic, load and season.
- Pick the unit in each field's menu (miles or kilometres, mpg or L/100 km); the calculator converts everything for you.
- Fill up to the brim twice and divide the distance by the fuel added to measure real fuel economy.
- For vehicle modifications, treat results as a starting point and confirm with the parts maker or a professional mechanic.

### Common mistakes to avoid

- Mixing US and imperial (UK) gallons – a UK gallon is about 20% bigger.
- Using the advertised fuel economy instead of real-world figures.
- Forgetting tolls, parking and wear and tear when comparing driving with public transport.

### Inputs explained

FieldWhat to enterRace weight (car + driver)Units: lb, kg, g, ozQuarter-mile elapsed timeIn sTrap speedUnits: mph, km/h, m/s, knots

### What each result means

- **Horsepower from elapsed time** = ([Race weight (car + driver)]÷0.45359237)÷([Quarter-mile elapsed time]÷5.825)^3
- **Horsepower from trap speed** = ([Race weight (car + driver)]÷0.45359237)×([Trap speed]÷0.44704÷234)^3
- **Trap-speed power in kW** = [Horsepower from trap speed]×0.74569987158227

### Example values

How the main result changes when **Quarter-mile elapsed time** changes and everything else stays at the example values above:

Quarter-mile elapsed time (s)Horsepower from elapsed time (hp)6.752,24910.1366613.528116.8814420.25832735

## Worked example

Inputs — Race weight (car + driver): 3,500 lb; Quarter-mile elapsed time: 13.5 s; Trap speed: 105 mph.

Results — **Horsepower from elapsed time = 281 hp**; Horsepower from trap speed = 316 hp; Trap-speed power in kW = 236 kW.

## FAQ

**Which formula is more accurate?**
The trap-speed formula, because a poor launch hurts elapsed time much more than trap speed.

**What ET does 400 hp give?**
A 3,500 lb car with 400 hp should run about 12.4 s in the quarter mile.

**Is this wheel or crank horsepower?**
The formulas approximate flywheel (crank) horsepower for a typical drivetrain.

**What formula does the Horsepower Calculator use?**
From elapsed time: hp = weight (lb) ÷ (ET ÷ 5.825)³.