Horsepower Calculator

Convert engine torque and RPM into horsepower with the standard SAE formula, then see wheel horsepower, kilowatts, and metric horsepower (PS).

Quick Facts

Formula
HP = Torque (lb-ft) x RPM / 5252
5252 is 33,000 ft-lb/min divided by 2 x pi — the constant that turns rotational torque and speed into horsepower.
Crossover point
Torque and HP are equal at 5252 RPM
Below 5252 RPM the torque number reads higher; above it, horsepower reads higher — an artifact of the formula, not the engine.

Your Results

Calculated
Crank horsepower
-
Torque x RPM / 5252
Wheel horsepower
-
After drivetrain loss estimate
Power in kilowatts
-
1 hp = 0.7457 kW
Metric horsepower (PS)
-
1 hp ≈ 1.0139 PS

Ready

Enter torque and RPM, then choose a drivetrain layout to estimate wheel horsepower.

About the Horsepower Calculator

This calculator converts engine torque and rotational speed into horsepower using the standard SAE (Society of Automotive Engineers) formula: HP = Torque (lb-ft) x RPM / 5252. It then estimates wheel horsepower after a chosen drivetrain loss, and converts the result to kilowatts and metric horsepower (PS) for comparison against European power ratings.

Where the formula comes from

One horsepower is defined as 33,000 foot-pounds of work per minute. Power delivered by a rotating shaft equals torque multiplied by angular speed: Power = Torque x RPM x 2 x pi (since each revolution sweeps 2 x pi radians). Dividing by 33,000 to convert to horsepower, and folding the constants together, gives Power (hp) = Torque x RPM / 5252.11 — rounded to 5252 in everyday use. This is the same formula dynamometer shops use to compute horsepower from a measured torque curve.

Crank horsepower vs. wheel horsepower

The torque/RPM formula gives crank horsepower — power at the engine's output shaft. Not all of that power reaches the pavement: the transmission, driveshaft, differential, and bearings absorb some as friction and heat before the wheels ever turn. Wheel horsepower is the more relevant number for real-world acceleration and dyno comparisons. This calculator approximates it using a drivetrain loss percentage: roughly 10% for front-wheel drive, 15% for rear-wheel drive, 20% for all-wheel drive, and 25% for four-wheel drive with a transfer case — widely used rule-of-thumb ranges rather than a measured value for any specific vehicle.

Converting to kilowatts and metric horsepower

Horsepower is a US customary unit; most of the world rates engine power in kilowatts or metric horsepower. The conversions are exact: 1 hp = 0.745699872 kW, and 1 hp ≈ 1.0139 PS (metric horsepower, defined as 735.49875 watts). These conversions do not depend on the drivetrain assumption — they simply re-express the same crank horsepower figure in different units.

How to get the best results

  • Use the torque figure at a specific RPM (peak torque, or any point on a dyno chart) — the formula gives instantaneous horsepower at that RPM, not an average across the whole rev range.
  • Torque must be in pound-feet (lb-ft); if you have Newton-meters, convert first by dividing by 1.3558.
  • The drivetrain loss estimate is a rough convention, not a measurement — an actual chassis dyno (which compares crank-rated horsepower to measured wheel horsepower) will give a more precise figure for a specific car.

Frequently Asked Questions

What is the formula for horsepower from torque and RPM?
Horsepower = Torque (lb-ft) x RPM / 5252. This is the standard SAE formula relating rotational torque and engine speed to mechanical power. The constant 5252 comes from converting torque and RPM into the definition of one horsepower (33,000 ft-lb per minute) using 2 x pi radians per revolution.
Why do torque and horsepower curves cross at 5252 RPM?
Because HP = Torque x RPM / 5252, whenever RPM equals 5252 the two values are numerically equal regardless of the actual torque curve. Below 5252 RPM the torque number reads higher than the horsepower number; above 5252 RPM horsepower reads higher. It is a mathematical artifact of the formula, not an engine characteristic.
What is the difference between crank horsepower and wheel horsepower?
Crank horsepower is the power measured at the engine's output shaft (from a dynamometer or the torque/RPM formula). Wheel horsepower is what actually reaches the road after the transmission, driveshaft, and differential absorb some power as friction and heat. A drivetrain loss estimate (commonly 10 to 25 percent depending on layout) approximates that difference.
How do kilowatts and metric horsepower (PS) relate to mechanical horsepower?
One mechanical horsepower equals 0.745699872 kilowatts. Metric horsepower (PS, or pferdestarke) is a slightly different unit defined as 735.49875 watts, so 1 mechanical hp equals about 1.0139 PS. The differences are small but matter when comparing US and European power ratings.

Related calculators