Horsepower Calculator

Torque is the rotational force the engine produces, measured in lb-ft or Nm. Horsepower is the rate at which work is done, calculated from torque and RPM using the formula: HP = (Torque × RPM) ÷ 5252. Torque is what you feel pushing you back in the seat during acceleration, while horsepower determines top speed and sustained performance. They are equal at 5,252 RPM.

Use the formula: Horsepower = (Torque × RPM) ÷ 5252. For example, if an engine produces 300 lb-ft of torque at 5,000 RPM: HP = (300 × 5000) ÷ 5252 = 286 HP. The constant 5252 comes from unit conversions (33,000 ft-lb per minute for 1 HP, divided by 2π for rotational conversion). This is why torque and horsepower curves cross at 5,252 RPM.

Yes, using the formula: HP = Weight ÷ (ET ÷ 5.825)³. For a 3,500 lb car running 14.5 seconds: HP = 3500 ÷ (14.5 ÷ 5.825)³ = approximately 285 HP. This is an estimate as it assumes typical drivetrain losses, traction, and aerodynamics. Actual horsepower can vary based on driver skill, tire grip, elevation, and weather conditions.

Power-to-weight ratio measures performance potential. In HP per 1,000 lbs: 50-70 is economy, 70-100 is average, 100-150 is sporty, 150-200 is high performance, and over 200 is supercar territory. A Mazda Miata has about 117 HP/1000 lbs, a Corvette around 175, and a Ferrari F8 exceeds 250. Lower weight is often more effective than more power for overall performance.

Trap speed (speed at the end of quarter mile) is one of the most accurate methods for estimating horsepower without a dyno. The formula HP = Weight ÷ (224 ÷ Trap Speed)³ accounts for the energy needed to accelerate the mass to that speed. It is more consistent than elapsed time because it is less affected by driver skill, launch technique, or traction issues at the start.

Brake horsepower (BHP) is measured at the engine flywheel before drivetrain losses. Wheel horsepower (WHP) is measured at the wheels after transmission, driveshaft, and differential losses. Typically, front-wheel drive loses 10-15%, rear-wheel drive loses 15-18%, and all-wheel drive loses 20-25%. A car rated at 300 BHP might produce 255 WHP at the wheels on a chassis dyno.

Naturally aspirated engines lose approximately 3% horsepower per 1,000 feet of elevation due to thinner air. At 5,000 feet, a 300 HP engine produces about 255 HP. Turbocharged engines are less affected because the turbo compensates for lower air density. High altitude also affects quarter mile times, adding roughly 0.2 seconds per 1,000 feet and reducing trap speed by 2-3 mph.

Manufacturers test engines under ideal SAE conditions: optimal temperature, no accessories, no exhaust restrictions. Real-world horsepower is often 5-10% lower due to air filter, full exhaust system, alternator load, cooling fan, and climate conditions. Some manufacturers also rate peak power optimistically. Dyno testing your specific vehicle gives the most accurate measurement of actual output.

For a 3,500 lb car: 12-second quarter mile needs about 400 HP, 11-seconds needs 500+ HP, 10-seconds needs 650+ HP. For 0-60 mph times: 6 seconds needs 250 HP, 5 seconds needs 320 HP, 4 seconds needs 450+ HP. These are estimates; actual performance depends heavily on traction, gearing, aerodynamics, and driver skill. Light cars need less power for the same times.

One horsepower equals 0.7457 kilowatts, and one kilowatt equals 1.341 horsepower. To convert: HP = kW × 1.341, or kW = HP × 0.7457. For example, 300 HP = 224 kW. Most European and Asian markets use kilowatts (kW) while North America uses horsepower (HP). Some manufacturers list both specifications for global markets.