Horsepower & Torque Calculator

Convert between horsepower, torque and engine speed. Enter any two and get the third, in both imperial (hp, lb-ft) and metric (kW, Nm) units — the relationship that connects every engine spec.

How to use this calculator

Choose whether to solve for horsepower, torque or RPM.
Enter the other two values (torque in lb-ft).
Read the result with metric (Nm, kW, PS) equivalents.

Formula used

Horsepower = Torque (lb-ft) × RPM ÷ 5252

The constant 5,252 comes from the definition of horsepower (33,000 ft-lb/min) divided by 2π. A consequence: horsepower and torque curves always cross at exactly 5,252 RPM on any engine, because that's where the formula makes them numerically equal.

Example calculation

Worked example

250 lb-ft at 4,200 RPM: hp = 250 × 4200 ÷ 5252 = 200 hp (149 kW). The torque is 339 Nm.

At exactly 5,252 RPM, any engine's hp and lb-ft figures are equal — a quirk of the formula, not a coincidence.

Torque vs horsepower

Torque and horsepower measure different things people often conflate. Torque is raw twisting force — what you feel as shove when accelerating, and what moves heavy loads. Horsepower is the rate of doing work: torque multiplied by how fast the engine spins. An engine can make big torque at low RPM (a diesel truck) or modest torque at very high RPM (a small sports engine) and reach similar horsepower by different routes.

The famous 5,252 RPM crossover isn't mysticism — it falls straight out of the formula, since horsepower = torque × RPM ÷ 5,252, so at 5,252 the two numbers are always equal. Below it, torque exceeds horsepower numerically; above it, horsepower pulls ahead. Understanding the relationship explains why peak-torque and peak-power figures occur at different RPMs, and why gearing (see the gear ratio calculator) is what turns either into usable acceleration.

Why use this calculator?

Convert any two of horsepower, torque and RPM into the third.
See imperial (hp, lb-ft) and metric (kW, Nm, PS) side by side.
Understand the 5,252 RPM crossover and what each spec means.

Frequently asked questions

How do I convert torque to horsepower?

Multiply torque in lb-ft by RPM, then divide by 5,252. So 300 lb-ft at 5,000 RPM = 300 × 5000 ÷ 5252 ≈ 286 hp. To go the other way, horsepower × 5,252 ÷ RPM gives torque.

Why do horsepower and torque cross at 5,252 RPM?

Because horsepower is defined as torque × RPM ÷ 5,252. At exactly 5,252 RPM the RPM and constant cancel, making the two numbers equal. It's a mathematical certainty on every engine's dyno chart, not a coincidence.

Is torque or horsepower more important?

Both matter differently. Torque gives low-end pulling power and the sense of shove; horsepower (torque sustained at high RPM) determines top speed and how power holds as revs climb. Trucks prize torque; sports cars chase horsepower. Gearing links the two to actual acceleration.