Horsepower Calculator
Calculate internal combustion engine mechanical horsepower, metric kilowatts (kW), and Pferdestärke (PS) directly from measured torque and RPM. Optionally estimate engine flywheel power from vehicle curb weight and quarter-mile elapsed times with instantaneous precision and zero server latency.
Peak or operating rotational force in pound-feet
Engine crankshaft rotational speed in RPM
Total curb weight including driver for quarter-mile drag estimation
Quarter-mile drag strip elapsed time in seconds
Calculated brake/flywheel mechanical horsepower
How to Use This Calculator
- Obtain your engine dyno torque measurement in pound-feet (lb-ft).
- Enter the exact engine RPM corresponding to that torque reading.
- Observe mechanical horsepower, metric kilowatts, and European PS instantly.
- Optionally enter total vehicle weight and drag strip 1/4 mile ET to estimate net power.
Formula & Calculation Methodology
Mechanical horsepower measures the rate of work done. Since 1 horsepower equals 33,000 foot-pounds per minute and circumference of 1-foot radius equals 2π feet, 33,000 ÷ 2π equates to the fundamental constant 5252.113.
Worked Example
350 lb-ft of torque at exactly 5,252 RPM in a 3,400 lb car running a 13.2s quarter-mile
Frequently Asked Questions
Why do torque and horsepower curves always intersect at exactly 5,252 RPM?↓
This is a mathematical certainty derived from the definition of mechanical horsepower: HP = (Torque × RPM) ÷ 5252. When RPM equals 5252, the RPM and denominator cancel out, meaning horsepower numerically equals torque in lb-ft.
What is the difference between Wheel Horsepower (WHP) and Crank/Brake Horsepower (BHP)?↓
Brake Horsepower (BHP) is measured directly at the engine flywheel with no drivetrain. Wheel Horsepower (WHP) is measured at the driving wheels via a chassis dyno and is typically 12% to 18% lower due to transmission, differential, and tire friction losses.
How does atmospheric elevation and temperature impact horsepower?↓
Naturally aspirated engines lose roughly 3% of their power output for every 1,000 feet of altitude gain due to lower atmospheric air density and reduced oxygen mass per cylinder intake charge.
What is the relationship between kilowatts (kW) and horsepower?↓
One mechanical horsepower equals 745.699872 watts (approximately 0.7457 kW). Conversely, 1 kilowatt equals 1.341 horsepower. Many global automotive markets (such as Australia and Europe) legally mandate kW on vehicle titles.
What limitation exists when calculating horsepower from quarter-mile times?↓
Quarter-mile time calculations assume optimal traction launch, quick shifting, and typical aerodynamic drag coefficients. Heavy wheel spin at launch will produce an artificially low horsepower estimate.
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Open calculator →Source Citation & Disclaimer
Informational tool only; not licensed tax, legal, or financial advice.