Horsepower Calculator

What is a horsepower calculator?

A horsepower calculator converts between an engine’s horsepower (HP), its torque in pound-feet (lb-ft) and its engine speed in revolutions per minute (RPM). Supply any two of the three and it returns the third, using the fixed relationship that ties rotating force to power. Engine builders, tuners, racers, students and curious owners use it to estimate output from a dyno torque reading, to work out how much torque a power target demands, or to settle the classic “what is the difference between horsepower and torque” question with real numbers.

Type your two known values into the tool above and it solves for the missing one immediately, with no sign-up and nothing leaving your browser.

How is horsepower calculated from torque and RPM?

The tool uses the standard relationship between rotating force and power:

HP = (torque [lb-ft] × RPM) ÷ 5252

Horsepower is rotational work done per unit time, so it depends on how hard the crankshaft twists (torque) and how fast it spins (RPM) together. Here is what every symbol means and the unit it carries:

• HP — horsepower, the power output. One horsepower is 33,000 foot-pounds of work per minute.
• torque — the twisting force at the crankshaft, in pound-feet (lb-ft). It must be a positive number, and non-zero when used as a divisor.
• RPM — engine speed in revolutions per minute, non-zero when used as a divisor.
• 5252 — the conversion constant. It comes from 33,000 ft-lb/min per horsepower divided by 2π (the radians in one revolution), so 33,000 ÷ 2π = about 5252.

Because the relationship is a single equation, it rearranges two ways so you can solve for whichever value you are missing:

You know	It finds	Using
torque and RPM	horsepower	HP = torque × RPM ÷ 5252
horsepower and RPM	torque	torque = HP × 5252 ÷ RPM
horsepower and torque	RPM	RPM = HP × 5252 ÷ torque

Why horsepower and torque meet at 5252 RPM

A neat consequence falls straight out of the formula. If RPM equals 5252, then RPM ÷ 5252 = 1, so HP equals torque numerically. That is why on every dyno chart the horsepower and torque curves cross at exactly 5252 RPM: below it torque reads higher than horsepower, above it horsepower reads higher than torque, and at 5252 RPM they are the same number.

The result is computed at full precision and rounded for display, for example to one decimal place such as 380.8 hp.

Examples

Each example uses only the formula above, so you can reproduce every answer by typing the same values into the calculator.

Example 1 — the 5252 RPM crossover

Torque 300 lb-ft, engine speed 5252 RPM.

HP = torque × RPM ÷ 5252 = 300 × 5252 ÷ 5252 = 300 hp

At exactly 5252 RPM the constant cancels, so 300 lb-ft produces 300 hp — horsepower and torque are numerically equal, just as the curves cross on a dyno plot.

Example 2 — horsepower from a dyno torque reading

Torque 400 lb-ft, engine speed 5000 RPM.

HP = 400 × 5000 ÷ 5252 = 2,000,000 ÷ 5252 = 380.8 hp

A peak of 400 lb-ft at 5000 RPM works out to about 380.8 horsepower. Because 5000 RPM is just below 5252, the horsepower figure lands a little under the torque figure.

Example 3 — finding the torque a power target needs

Horsepower 300, engine speed 6000 RPM. Here we rearrange to solve for torque.

torque = HP × 5252 ÷ RPM = 300 × 5252 ÷ 6000 = 1,575,600 ÷ 6000 = 262.6 lb-ft

To make 300 hp at 6000 RPM an engine needs about 262.6 lb-ft of torque. Spinning faster lets a smaller torque produce the same power, which is why high-revving engines can be powerful without huge torque numbers.

Example 4 — solving for RPM

Horsepower 300, torque 300 lb-ft. This time we solve for engine speed.

RPM = HP × 5252 ÷ torque = 300 × 5252 ÷ 300 = 5252 RPM

Whenever horsepower and torque share the same number, the engine speed must be 5252 RPM — the only point where the two are equal.

Horsepower at a fixed torque: an RPM reference

This chart holds torque constant at 300 lb-ft and steps the RPM up, computing horsepower from 300 × RPM ÷ 5252. It shows how the same torque makes more power the faster it is delivered, and confirms the 5252 RPM crossover where HP equals the 300 lb-ft figure.

Torque (lb-ft)	Engine speed (RPM)	Horsepower (HP)
300	2000	114.2
300	3000	171.4
300	4000	228.5
300	5252	300.0
300	6000	342.7
300	7000	399.8

Notice the horsepower equals the torque (300) exactly at 5252 RPM, reads lower below it and higher above it — the same pattern you see where dyno curves cross.

Common uses

The horsepower calculator earns its place anywhere rotating power matters:

• Reading a dyno sheet — convert a measured peak torque and the RPM it occurs at into peak horsepower, or check a quoted HP figure.
• Setting a build target — work backwards from a horsepower goal to the torque or RPM an engine must reach.
• Comparing engines — see why a high-revving engine and a low-revving one can make the same horsepower from very different torque.
• Education and exams — automotive and physics coursework that links torque, speed and power.
• Tuning decisions — judge whether more power should come from more torque or from raising the RPM where torque is made.
• Curiosity — answer the perennial torque-versus-horsepower debate with the actual equation.

Tips and common mistakes

• Use pound-feet, not newton-metres. The 5252 constant is built for torque in lb-ft and speed in RPM. Convert newton-metres to lb-ft (divide by about 1.3558) before entering, or the result is wrong.
• Pound-feet, not foot-pounds of energy. Engine torque is lb-ft (force times lever arm); do not confuse it with the foot-pound unit of work or energy, even though the words look similar.
• Match the RPM to the torque. Use the engine speed at which that torque is actually produced. Peak torque and peak horsepower usually occur at different RPM, so do not mix one engine’s torque with another’s RPM.
• Do not divide by zero. Finding torque needs a non-zero RPM, and finding RPM needs a non-zero torque. Zero in a divisor makes the result undefined.
• Remember the 5252 crossover. If your computed horsepower is higher than torque, the RPM must be above 5252; if lower, below it. A result that breaks this pattern signals a units mistake.
• This is crankshaft power, not wheel power. The figure is gross engine output. Power measured at the wheels is lower because of drivetrain losses.

Limitations and notes

This calculator gives the exact mathematical relationship between horsepower, torque and RPM at a single operating point; it does not model an engine. It returns the power that a given torque produces at a given speed, but it cannot tell you how much torque your engine actually makes at that RPM — that comes from a dyno or the manufacturer’s curve. The result is crankshaft (gross) horsepower and does not subtract drivetrain, accessory or friction losses, so wheel horsepower will read lower. It assumes torque is entered in pound-feet and speed in RPM, the units the 5252 constant requires; SI inputs must be converted first. Everything runs privately in your browser — the values you type stay on your device, the math is computed at full precision and only rounded for display, and nothing is uploaded. Treat the output as an accurate conversion between the three quantities rather than a prediction of real-world engine output.

For related engine math, find swept volume with the engine displacement calculator, set squeeze with the compression ratio calculator, or convert road speeds with the speed converter — and browse more in the automotive category.