Last updated October 5, 2026 · Report an error
When a dyno isn't available, drag racers commonly estimate a vehicle's net flywheel horsepower from just two numbers: its weight and its quarter-mile elapsed time. This is distinct from the site's Horsepower Calculator, which derives horsepower from torque and RPM measured on a dyno.
This calculator applies the widely used "ET method" formula to give a quick horsepower estimate from a time slip and a scale weight.
How it works
Enter the vehicle's weight in pounds and its quarter-mile elapsed time in seconds. The calculator divides the weight by the elapsed time (scaled by a fixed constant) cubed, giving an estimated horsepower figure.
- Enter vehicle weight (lbs).
- Enter quarter-mile elapsed time (seconds).
- Click Calculate to see your results.
Examples
A mid-13-second car
A 3,200 lb car running a 13.5 second quarter mile is estimated at roughly 257 horsepower.
Who should use it
- Estimating a car's horsepower after a quarter-mile time slip.
- Comparing estimated horsepower across different runs or vehicles.
Industry applications
- Automotive performance and drag racing
- Vehicle tuning and modification
Advantages
- Estimates horsepower from just two easily obtained numbers.
- No dyno access required.
- No account, subscription or watermark.
Limitations
- Less precise than an actual dyno measurement — traction and driving technique affect elapsed time.
Common mistakes to avoid
- Using trap speed instead of elapsed time — this calculator specifically uses the ET method, not the trap-speed method.
- Forgetting to include driver and fuel weight in the vehicle weight figure.
Best practices
- Use an accurate scale weight that includes the driver and a full tank of fuel.
- Treat the result as a ballpark estimate, not a precise dyno-equivalent figure.
Tips
- Run the calculation across several time slips and average the results for a more reliable estimate.
- Weigh the vehicle with a full tank and driver aboard for the most accurate input weight.