What this calculator does
This tool converts engine torque and rotational speed into horsepower using the standard automotive formula. Enter your engine's torque (in pound-feet) and peak RPM, and instantly see the power output in HP. It's useful for comparing engines, understanding dyno results, or estimating performance.
The relationship between torque and power
Torque alone doesn't tell you how powerful an engine is—you also need to know how fast it spins. A small engine spinning at 8,000 RPM can produce more horsepower than a large, heavy engine at 2,000 RPM, even if both have identical torque. Horsepower captures both the rotational force and the speed at which that force is applied, giving a complete picture of power output.
The formula
HP = (Torque × RPM) ÷ 5,252
The constant 5,252 is a unit-conversion factor specific to imperial measurements (lb-ft and RPM). It comes from the relationship between mechanical power (in foot-pounds per minute) and rotational motion (in radians per second).
Worked example
Let's say you have a gasoline engine that produces 350 lb-ft of torque at 5,500 RPM.
Step 1: Multiply torque by RPM
350 × 5,500 = 1,925,000
Step 2: Divide by 5,252
1,925,000 ÷ 5,252 = 366.4 HP
So this engine generates approximately 366 horsepower at its peak torque RPM.
Now compare a turbocharged diesel with 600 lb-ft at 2,000 RPM:
600 × 2,000 = 1,200,000
1,200,000 ÷ 5,252 = 228 HP
Despite having much higher torque, the diesel produces less peak horsepower because it spins more slowly. However, that high torque at low RPM makes it excellent for towing and hauling—a different measure of usefulness.
Practical insight: torque curve vs. peak power
Real engines don't produce the same torque across all RPM ranges. Most gasoline engines peak in torque somewhere in the middle of their operating range (3,000–5,500 RPM), then torque drops as RPM climbs. Horsepower, however, often continues rising toward redline because the RPM multiplier overcomes the falling torque.
This is why you'll see engine spec sheets listing both "350 lb-ft @ 4,200 RPM" and "420 HP @ 6,200 RPM." At 4,200 RPM, torque is at its maximum but RPM is still relatively low. By 6,200 RPM, torque has declined, but the higher speed produces more power. Racers and performance tuners obsess over the shape of the torque curve, not just the peak—a flat, broad torque band means usable power across a wide RPM range.
Common mistakes
Confusing peak torque RPM with peak power RPM: They're usually different. Calculate HP at several points across the RPM range to see where true peak power occurs.
Forgetting to convert units: This formula requires torque in pound-feet and RPM as a simple number. If you have torque in Newton-meters, convert first (1 lb-ft ≈ 1.356 N⋅m).
Assuming higher torque always means more power: Not true at the same RPM. Context matters—a truck engine and a sports car engine might have similar peak torque but vastly different peak HP due to their different RPM characteristics.
Note: This is a mathematical estimate based on the standard SAE formula. Actual engine output varies with temperature, fuel quality, altitude, and drivetrain losses.