Calculate horsepower from torque, trap speed or quarter-mile ET.
Calculated instantly in your browser.
How is horsepower calculated?
From torque: HP = torque × RPM ÷ 5252. You can also estimate it from drag-strip results: HP = weight × (mph ⁄ 234)³ from trap speed, or HP = weight × (5.825 ⁄ ET)³ from elapsed time. Power and torque are equal at 5,252 rpm, so 300 lb-ft at that speed is exactly 300 hp.
Understanding your result
Power and torque are equal at 5,252 rpm, which is where their curves cross. The trap-speed and ET formulas are empirical estimates of flywheel power from drag-strip performance, so they are approximate.
Formula and method
From torque: HP = torque × RPM ÷ 5252. From trap speed: HP = weight × (mph ⁄ 234)³. From ET: HP = weight × (5.825 ⁄ ET)³.
Assumptions and limitations
The trap-speed and elapsed-time methods are empirical estimates of flywheel power from drag-strip figures, so they are approximate and sensitive to accurate weight and clean runs. Traction, aerodynamics, altitude and driver skill all shift the result. The torque-and-rpm method is exact only for the inputs given and does not measure losses through the drivetrain.
Worked example
300 lb-ft at 5,252 rpm is exactly 300 hp; a 3,000 lb car trapping 100 mph is roughly 234 hp.
How to use this tool
- Choose torque, trap speed or ET.
- Enter the matching values.
- Read the horsepower estimate.
Common mistakes to avoid
- Mixing wheel horsepower with crank (flywheel) horsepower.
- Using metric torque units — these formulas expect lb-ft and lb.
About the Horsepower Calculator
The Horsepower Calculator finds engine horsepower from torque and RPM, or estimates it from a vehicle’s weight and quarter-mile trap speed or elapsed time (ET).
Who should use this tool
Car enthusiasts, racers and anyone curious about engine power.
Benefits
- Three ways to calculate horsepower.
- Results in hp, kW and metric PS.
- Shows the formula used.
- Instant and private.
Practical use cases
- Converting a dyno torque figure to horsepower.
- Estimating power from a drag-strip run.
- Comparing engine outputs.
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Frequently asked questions
Why is power equal to torque at 5252 rpm?
Because of the constant in the formula HP = torque × RPM ÷ 5252; at 5,252 rpm the multiplier is one, so the two values match.
Are the trap-speed estimates accurate?
They give a good ballpark of flywheel power but depend on traction, aerodynamics and conditions, so treat them as estimates.
Why do the three methods give different horsepower figures?
The torque-and-rpm calculation is a direct definition of power, while the trap-speed and elapsed-time formulas infer power from how a whole vehicle performs. Because those depend on weight, traction and conditions, they estimate flywheel power indirectly and can differ from the torque-based figure.