Quarter mile calculator
Enter the weight of the car with the driver and its power in horsepower. The calculator estimates the quarter-mile elapsed time and the speed at the finish using two empirical rules of thumb. They are estimates for a well-prepared run, and real results vary with traction, gearing, altitude and the driver.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Pick kilograms or pounds and enter the weight of the car including the driver and fuel.
- Enter the power in horsepower.
- Read the estimated elapsed time and trap speed.
How it works
The weight is converted to pounds, then:
- ET = 5.825 × (weight ÷ hp)^(1/3) seconds.
- Trap speed = 234 × (hp ÷ weight)^(1/3) mph.
Both depend only on the weight-to-power ratio, so halving the weight has the same effect as doubling the power.
Worked example
A 3,000 lb car with 300 hp has 10 lb per hp. The cube root of 10 is 2.154, so the ET is 5.825 × 2.154 = 12.55 s and the trap speed is 234 ÷ 2.154 = 108.6 mph (174.8 km/h).
Tips
- Include the driver and a typical fuel load in the weight.
- Treat it as a comparison tool. The same formula applied to two setups shows which is faster even if both numbers are slightly off.
Frequently asked questions
Which formulas does the calculator use?
ET in seconds = 5.825 × (weight in pounds ÷ horsepower)^(1/3), and trap speed in mph = 234 × (horsepower ÷ weight in pounds)^(1/3). They are old empirical rules fitted to many street and race cars.
How accurate is the estimate?
It is an estimate only. Tyres, launch technique, gearing, drive type, weather and the track surface can change a real time by a second or more. Use it to compare cars or modifications, not to promise a time.
Should I enter engine power or wheel power?
The formulas are usually quoted for power at the wheels or for a net engine rating on a typical car. If you enter flywheel horsepower, expect the real car to be a little slower than the estimate because of drivetrain losses.
How do I convert kW or PS to hp?
Multiply kilowatts by 1.341 to get mechanical horsepower. Metric horsepower (PS) is about 0.986 mechanical hp.