Free engine horsepower calculator
Enter torque and RPM — this engine horsepower calculator applies the SAE formula (hp = torque × RPM ÷ 5,252) to find crank power and convert between hp, kW, and PS, updated live, as you type.
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hp = torque × RPM ÷ 5252. 1 mechanical horsepower = 0.7457 kW (SAE).
Results are estimates. Consult a professional.
How the engine horsepower calculator works
Engine horsepower is always measured at the crankshaft — often called crank HP or brake horsepower (BHP). It is calculated from two values any performance dyno measures simultaneously: torque (in pound-feet) and engine speed (RPM). The relationship is defined by a universal constant derived from the physics of rotational work.
Since 1972, all US manufacturer power ratings follow the SAE J1349 net standard: the engine is tested fully dressed — alternator, air cleaner, power steering pump, exhaust system, and all belt-driven accessories installed — at controlled ambient conditions. Earlier SAE gross ratings stripped these accessories, producing inflated numbers that can be 20–50% higher than the equivalent net figure for the same engine.
SAE J1349: Engine Power Test Code — Spark Ignition and Compression IgnitionWorked example: Mustang Shelby GT500 at peak power
Ford rates the 2024 Shelby GT500's supercharged 5.2-liter V8 at 625 lb-ft of torque at 4,500 RPM. Use the formula to verify the claimed 760 hp at 7,300 RPM, and calculate power at the torque peak.
Famous engines: crank HP, torque, and redline
The table below lists crank horsepower, peak torque, and redline RPM for some of the most celebrated production car engines. All figures are SAE J1349 net certified unless noted.
| Engine / Vehicle | Crank HP | Peak Torque (lb-ft) | Redline (RPM) |
|---|---|---|---|
| Chevy Corvette Z06 (LT6 5.5L NA) | 670 | 460 | 8,600 |
| Ford Shelby GT500 (5.2L SC) | 760 | 625 | 7,500 |
| Dodge Hellcat Redeye (6.2L SC) | 797 | 707 | 6,200 |
| Ferrari 296 GTB (3.0L V6 Hybrid) | 819 | 546 | 8,500 |
| Lamborghini Huracán EVO (5.2L V10) | 631 | 442 | 8,500 |
| Bugatti Chiron (8.0L W16 Quad-Turbo) | 1,479 | 1,180 | 6,700 |
| Dodge Demon 170 (6.2L SC) | 1,025 | 945 | 6,500 |
Source: Manufacturer press kits; SAE J1349 certified. Ferrari output includes hybrid motor assist.
Tips for reading engine horsepower specs
Engine HP claims are everywhere, but not all numbers are created equal. These tips help you cut through the marketing and understand what you're actually comparing.
- Always ask: net or gross? — Pre-1972 US gross ratings are not comparable to modern net SAE figures. A 1970 muscle car rated at 450 gross hp might be closer to 340–370 hp on today's SAE net standard.
- Crank HP vs. wheel HP — Manufacturers quote crank (flywheel) output. Plan for 10–20% less at the drive wheels depending on drivetrain type. Use a chassis dyno for real-world verification.
- Hybrid system horsepower — Modern hybrids (Ferrari, Porsche, Lamborghini) add electric motor output to combustion engine output. The combined figure is usually what's advertised — confirm whether the spec is combined or combustion-only.
- Premium fuel matters — Many high-performance engines are rated on 91–93 octane premium fuel. Running regular 87 octane triggers knock retard and can reduce output by 5–15% in high-compression or boosted engines.
- Altitude derating — Naturally aspirated engines lose ~3% power per 1,000 ft of elevation. If you're comparing dyno numbers from Denver (5,280 ft) to sea-level results, apply a correction factor before drawing conclusions.
Accuracy and limitations
The hp = torque × RPM ÷ 5,252 formula is exact — there is no approximation. The uncertainty lies entirely in the accuracy of your torque and RPM inputs. Engine dynamometer readings are highly reliable when the equipment is calibrated, but even professional-grade dynos can vary ±1–2% between runs due to temperature, humidity, and fuel quality differences.
Using manufacturer-published torque to reverse-engineer peak horsepower will match the rated figure closely but won't reproduce the full power curve. Engines produce different torque values at every RPM step; a single torque-at-peak figure only tells you the horsepower at that RPM. To reconstruct a complete curve you need data at every RPM interval, as plotted by a full dyno pull.
Engine power terms defined
About this engine horsepower calculator
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