HP from Torque & RPM Calculator
Instantly calculate engine horsepower using the industry-standard 5252 rule.
This horsepower from torque and RPM calculator converts engine torque (in pound-feet) and engine speed (in revolutions per minute) into horsepower using the standard 5252 rule. It is the same relationship every chassis and engine dynamometer uses to plot a power curve, so it works equally well for a street car, a race engine, or an electric motor rated in lb-ft.
The Horsepower from Torque & RPM Formula
The constant 5252 is not arbitrary. Horsepower is defined as 33,000 foot-pounds of work per minute, and one full revolution sweeps through 2π radians. Dividing 33,000 by 2π gives 5252.11, the conversion factor that links rotational torque to power. Because both horsepower and torque share this constant, their curves on a dyno graph always cross at exactly 5252 RPM — a useful sanity check when you read any power chart.
If your torque figure is in newton-metres (Nm) instead of pound-feet, convert first (1 Nm = 0.7376 lb-ft) or use the metric form: kW = (Torque [Nm] × RPM) ÷ 9549, then convert kilowatts to horsepower.
How to Use This Calculator
- Enter torque in pound-feet. This is your engine's measured or rated torque — from a dyno sheet, a manufacturer spec, or a torque-to-HP estimate.
- Enter engine speed in RPM, ideally the RPM at which that torque figure was recorded (peak-torque RPM gives peak figures).
- Read the horsepower result instantly. Use the copy or share buttons to save or send the calculation.
Worked Example
The example shows why high-revving engines make big horsepower even with modest torque: a small motorcycle engine producing 90 lb-ft at 11,000 RPM still makes roughly 188 HP, while a diesel making 1000 lb-ft at only 1800 RPM makes about 343 HP. Horsepower is the rate at which torque is delivered, which is why RPM matters as much as the torque itself.
Torque vs Horsepower: What's the Difference?
Torque is the rotational force an engine produces — what you feel as low-end pull. Horsepower is how quickly that work is done over time. For a deeper explanation of why the two curves meet at 5252 RPM and which matters for acceleration, see our guide on horsepower vs torque and the 5252 rule explained. If you only have a horsepower figure and need torque instead, use the reverse HP to torque calculator.
This calculator applies the exact mathematical 5252 relationship. The horsepower figure is only as accurate as the torque and RPM you enter — measured dyno values give real results, while rated specs give estimates. Drivetrain losses are not deducted here; for power at the wheels, use the wheel horsepower calculator.
Why HP and Torque Always Cross at 5,252 RPM
Because HP = Torque × RPM ÷ 5,252, the two curves are mathematically forced to intersect where RPM equals 5,252 — below it torque is the bigger number, above it horsepower is. If a dyno chart's curves don't cross there (and both are in lb-ft and HP), something is mislabeled.
Illustrative curve shapes — every engine's actual curves differ, but the crossing point never moves.
Solve for Any of the Three Variables
The same relationship rearranges to answer all three common questions:
| You want | Formula | Example |
|---|---|---|
| Horsepower | HP = T × RPM ÷ 5252 | 420 lb-ft @ 4600 → 368 HP |
| Torque | T = HP × 5252 ÷ RPM | 480 HP @ 7250 → 348 lb-ft |
| RPM | RPM = HP × 5252 ÷ T | 400 HP with 400 lb-ft → 5252 |
Real Engines: Published Peaks vs. the Formula
A subtlety people miss: peak HP and peak torque occur at different RPM, so you cannot plug peak torque and redline into the formula. HP at any point uses the torque at that same RPM:
| Engine (published, approx.) | Peak torque | Peak power | What the formula shows |
|---|---|---|---|
| Ford 5.0 "Coyote" V8 | 415 lb-ft @ 4,900 | 480 HP @ 7,250 | At 7,250 RPM torque has fallen to ~348 lb-ft (348 × 7250 ÷ 5252 ≈ 480) |
| Chevrolet LS3 6.2 V8 | 424 lb-ft @ 4,600 | 430 HP @ 5,900 | At 5,900 RPM torque is ~383 lb-ft (383 × 5900 ÷ 5252 ≈ 430) |
| Cummins 6.7 turbodiesel | 1,075 lb-ft @ 1,800 | 420 HP @ 2,800 | Huge torque at low RPM still means modest HP: 1075 × 1800 ÷ 5252 ≈ 368 |
This is why diesels tow (torque at working RPM) while sports cars rev (holding torque up high multiplies into big horsepower). For rating-condition details (temperature, pressure corrections), manufacturers publish figures per SAE J1349 — see our SAE horsepower page.
Sources: 5,252 = 33,000 ft-lb/min ÷ 2π (James Watt's horsepower definition); SAE J1349 engine power rating standard; manufacturer published engine specifications (approximate).
Frequently Asked Questions
It is the mathematical constant used to convert torque into horsepower. Since 1 HP equals 33,000 ft-lb/min, and one revolution equals 2π radians, 33000 / (2×π) = 5252.11.
Yes, mathematically speaking. On any dyno graph displaying horsepower and torque in lb-ft on the same scale, the two lines must intersect exactly at 5252 RPM.
Pound-feet (lb-ft) is a unit of torque representing one pound of force applied one foot from the pivot point.
Convert newton-metres to pound-feet first by multiplying by 0.7376 (e.g. 542 Nm × 0.7376 ≈ 400 lb-ft), then enter the result. Alternatively use the metric formula kW = (Nm × RPM) ÷ 9549 and convert kilowatts to horsepower with our HP to kW tool.
Yes. If you know the motor's torque in lb-ft and its RPM, the same 5252 formula applies. Electric motors often make peak torque from zero RPM.