Calculate horsepower from torque and RPM using the standard formula. Convert between HP, kW, PS, and estimate quarter-mile times.
Horsepower is the universal measure of engine output, but understanding the relationship between torque and RPM is key to reading dyno sheets and comparing engines. This horsepower calculator uses the fundamental formula HP = Torque × RPM ÷ 5,252 to convert between torque and horsepower at any engine speed.
The magic number 5,252 is where the horsepower and torque curves always cross on a dyno chart — it's derived from the unit conversion: 1 HP = 33,000 ft·lb/min, and RPM converts rotational speed to linear equivalent. This calculator also handles metric conversions (kW, PS/DIN), drivetrain losses for wheel vs. crank horsepower, and weight-to-power ratio calculations.
Beyond simple conversion, the tool estimates quarter-mile performance using the Brock Yates / Roger Huntington empirical formula, calculates power-to-weight ratios, and generates a power curve table across the RPM range. Whether you're tuning an engine, comparing cars, or studying for an engineering exam, this gives you the complete picture.
Use this calculator when you want to move cleanly between torque, RPM, and horsepower without relying on a dyno chart screenshot or rough mental math. It is useful for tuning discussions, spec-sheet comparisons, and quick performance estimates tied to real engine speed. That makes it easier to compare engine output at a specific RPM instead of guessing from the peak number alone.
HP = Torque (lb-ft) × RPM ÷ 5,252. Metric: kW = Nm × RPM ÷ 9,548.8. PS (DIN) = HP × 1.01387. Wheel HP = Crank HP × (1 − Drivetrain Loss %). Quarter-mile (sec) ≈ 5.825 × (Weight / HP)^(1/3).
Result: 333.2 HP (248.5 kW, 337.8 PS)
350 lb-ft × 5000 RPM ÷ 5252 = 333.2 HP. Converting: 333.2 × 0.7457 = 248.5 kW. 333.2 × 1.01387 = 337.8 PS. Quarter mile ≈ 5.825 × (3500/333.2)^0.333 = 13.2 sec.
James Watt coined "horsepower" in the late 18th century to market his steam engines. He observed that a draft horse could do 33,000 foot-pounds of work per minute — turning a mill wheel. This became 1 mechanical horsepower. While Watt's measurement was generous (most horses sustain about 0.7 HP long-term, with bursts up to 14.9 HP), the unit stuck and became the standard for engine power worldwide.
Brake Horsepower (BHP) is measured at the crankshaft with no accessories attached. Wheel Horsepower (WHP) is measured at the tires via a chassis dynamometer. The difference is drivetrain loss. SAE Net Horsepower (used since 1972 in the US) includes standard accessories (alternator, exhaust, etc.). SAE Gross Horsepower (pre-1972) measured with minimal accessories, producing inflated numbers — a "350 HP" 1968 Corvette likely made about 270 SAE Net.
A dyno chart plots torque and horsepower against RPM across the engine's operating range. The torque curve shows where the engine's "grunt" is — useful for acceleration and towing. The horsepower curve, being torque × RPM, always rises above torque at high RPM. A flat, wide torque curve means a flexible, easy-to-drive engine. A peaky torque curve with a sharp HP rise means a performance-oriented engine that rewards high RPM driving.
The number 5,252 comes from unit conversion: 1 HP = 33,000 ft·lb per minute. Since torque × RPM / 33,000 × 2π gives power, the crossing point is 33,000 / (2π) ≈ 5,252 RPM where numerical torque equals numerical HP in imperial units.
Crank (brake) horsepower is measured at the flywheel. Wheel horsepower is what reaches the tires after drivetrain losses. Manual transmissions lose ~10-12%, automatics ~13-18%, and AWD systems ~18-25%.
Almost. PS (Pferdestärke, German for horsepower) is the metric equivalent. 1 PS = 0.9863 HP. The difference is ~1.4%. European car specs use PS while American specs use HP.
Torque depends on displacement and combustion pressure. HP depends on torque AND RPM. Small turbo engines make high torque at low RPM. High-revving naturally aspirated engines (like Honda VTEC) make peak HP at high RPM with moderate torque.
The empirical formula is accurate within ±0.5 seconds for production cars in the 10-16 second range. It doesn't account for traction, gearing, or aerodynamics, so heavily modified or very light cars may differ more.
Electric motors produce maximum torque from 0 RPM, then torque drops as speed increases (constant power region). The HP calculation is the same formula, but the torque curve shape is fundamentally different from combustion engines.