Horsepower Calculator

Compute mechanical power from torque + RPM (rotational) or force + velocity (linear). Instantly convert between horsepower (HP), kilowatts (kW), and metric horsepower (PS).

lb·ft
Pound‑feet (lb·ft) — standard automotive torque unit
rev/min
Engine / shaft revolutions per minute
?️ Sports car: 400 lb·ft @ 6000 RPM
? Sedan: 180 lb·ft @ 4500 RPM
⚙️ Industrial motor: 100 lb·ft @ 1750 RPM

What is Horsepower? Engineering Definition & History

The term horsepower (hp) was coined by Scottish engineer James Watt (1736–1819) to market his improved steam engines. Watt determined that a draft horse could perform 33,000 foot-pounds of work per minute, establishing the mechanical horsepower standard: 1 hp = 550 ft·lbf/s = 745.7 watts. Today, horsepower remains the dominant power unit for automotive engines, industrial machinery, marine propulsion, and electric motors—alongside the SI unit kilowatt (kW).

Core Formulas (Authoritative per SAE & ISO)

  • Rotational Power: \( HP = \frac{T \times \text{RPM}}{5252} \) where T = torque (lb·ft), RPM = revolutions/minute. The constant 5252 derives from \( \frac{33,000}{2\pi} \).
  • Linear Power (Imperial): \( HP = \frac{F \times v}{33,000} \) with F in lbf, v in ft/min.
  • SI Linear Power: \( P(W) = F(N) \times v(m/s) \), then convert: \( HP = P(W) / 745.7 \).

This calculator implements both methods with high precision, handling conversions for force (lbf/N) and velocity (ft/min, ft/s, mph, m/s), ensuring accurate engineering-grade results.

Real‑World Applications: Why Accurate Power Matters

Automotive & Motorsport

Dyno testing measures wheel horsepower. Knowing crankshaft HP helps calibrate ECU, optimize torque curves, and predict quarter-mile performance.

Industrial Machinery

Conveyor belts, hoists, and pumps require correct HP ratings to avoid motor overload. Linear HP formula prevents mechanical failures.

Marine & Aerospace

Propeller shaft power (SHP) relates to torque and RPM; regulatory bodies (ABS, FAA) use HP/kW for certification.

Performance Table: Typical Power Benchmarks

Application Torque (lb·ft) RPM Horsepower kW
Compact car (1.5L turbo) 185 5500 193.7 hp 144.4 kW
Motorcycle (600cc sport) 48 12500 114.2 hp 85.1 kW
Diesel truck (6.7L) 850 2800 453 hp 338 kW
Electric motor NEMA frame 175 1800 60 hp 44.7 kW

Frequently Asked Questions

Since 1 HP = 33,000 ft·lbf/min and power = torque (lb·ft) × angular speed (rad/min). Angular speed rad/min = RPM × 2π. Therefore HP = (Torque × RPM × 2π) / 33,000 = (Torque × RPM) / (33,000/(2π)) = (Torque × RPM) / 5252.113... (rounded to 5252).

bhp (brake horsepower) measures engine power at the flywheel without drivetrain loss. whp (wheel horsepower) is measured at the wheels after losses. This calculator computes mechanical horsepower equivalent to bhp/crank HP for given torque and RPM.

Absolutely. For electric motors, torque (lb·ft) and RPM yield output shaft horsepower. For linear actuators, use force (N or lbf) and velocity (m/s or ft/min). The calculator also shows kW for direct comparison to motor nameplates.

Yes. 1 metric horsepower (PS) = 735.5 watts, whereas 1 imperial HP = 745.7 W. Our tool displays both for global compatibility.
Engineering sources & references: Based on SAE J1349, ISO 1585, and standard mechanical engineering principles (Beer & Johnston, "Vector Mechanics"). Data verification performed using NIST physical constants. Last review: June 2026.
Instant kW ↔ HP Converter
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1 hp = 0.7457 kW | 1 kW = 1.34102 hp