Convert RPM to hp from shaft torque, or find the RPM or torque for a given horsepower, with results in hp, kW or PS and torque in lbf·ft or N·m.
| Torque + RPM to HP | HP + RPM to Torque |
|---|---|
| 100 lb-ft @ 2000 RPM = 38.1 HP | 5 HP @ 1750 RPM = 15.0 lb-ft |
| 150 lb-ft @ 2500 RPM = 71.4 HP | 10 HP @ 1800 RPM = 29.2 lb-ft |
| 200 lb-ft @ 3000 RPM = 114.2 HP | 15 HP @ 3600 RPM = 21.9 lb-ft |
| 250 lb-ft @ 4000 RPM = 190.4 HP | 20 HP @ 3000 RPM = 35.0 lb-ft |
| 300 lb-ft @ 3500 RPM = 199.9 HP | 25 HP @ 1725 RPM = 76.1 lb-ft |
| 300 lb-ft @ 5252 RPM = 300.0 HP | 30 HP @ 540 RPM = 291.8 lb-ft |
| 400 lb-ft @ 4500 RPM = 342.7 HP | 45 HP @ 1000 RPM = 236.3 lb-ft |
| 450 lb-ft @ 5500 RPM = 471.2 HP | 60 HP @ 2000 RPM = 157.6 lb-ft |
| 500 lb-ft @ 6000 RPM = 571.2 HP | 125 HP @ 3600 RPM = 182.4 lb-ft |
| 700 lb-ft @ 2100 RPM = 279.9 HP | 300 HP @ 6000 RPM = 262.6 lb-ft |
| Mechanical hp = T × RPM × 2π / 33,000; torque T in lbf·ft. | |
| Torque + RPM to kW | kW + RPM to Torque |
|---|---|
| 100 N·m @ 1500 RPM = 15.7 kW | 1.5 kW @ 1500 RPM = 9.5 N·m |
| 200 N·m @ 2000 RPM = 41.9 kW | 5.5 kW @ 1500 RPM = 35.0 N·m |
| 300 N·m @ 3000 RPM = 94.2 kW | 11 kW @ 1480 RPM = 71.0 N·m |
| 400 N·m @ 4000 RPM = 167.6 kW | 22 kW @ 2950 RPM = 71.2 N·m |
| 500 N·m @ 5000 RPM = 261.8 kW | 45 kW @ 3000 RPM = 143.2 N·m |
| 600 N·m @ 2500 RPM = 157.1 kW | 75 kW @ 3600 RPM = 198.9 N·m |
| kW = T × RPM × 2π / 60,000; torque T in N·m. | |
RPM to Horsepower Formula
Where HP is mechanical horsepower, T is torque in lbf·ft, and RPM is revolutions per minute. In SI units, power in watts is torque in N·m times angular speed in rad/s. Thus kW = T × RPM × 2π / 60,000 for torque in N·m. The familiar divisors 5252 and 9549.3 are rounded shortcuts; this calculator retains full π.
Where Does the 5252 Constant Come From?
One mechanical horsepower is 33,000 ft·lbf/min, or 550 ft·lbf/s. Work per revolution at constant torque is 2π times torque; multiplying by RPM gives work per minute. The horsepower divisor is 33,000/(2π) ≈ 5252.113122. The corresponding kW divisor for N·m and RPM is 60,000/(2π) ≈ 9549.296586.
The 5252 RPM Crossover Point
Mechanical horsepower and positive torque in lbf·ft have equal numerical values near 5252.11 RPM. Their plotted curves intersect there only if that operating point exists and both use the same numerical vertical scale. Below this speed the positive torque number is higher; above it the horsepower number is higher. This comparison follows from the unit definitions, not an engine design feature.
Types of Horsepower
Not all horsepower ratings measure the same thing. The type depends on where in the drivetrain power is measured and which unit system applies.
| Type | Abbr | Definition | Watts per unit |
|---|---|---|---|
| Mechanical | hp | 33,000 ft-lbf/min (Watt’s standard) | 745.70 |
| Metric | PS | 75 kgf-m/s (EU/Japan ratings) | 735.50 |
| Electrical | hp(E) | Distinct electrical-horsepower unit | 746.00 |
| Brake | BHP | Crankshaft/flywheel output via dyno | 745.70 per mechanical hp |
| Indicated | IHP | Cylinder pressure power, pre-friction | 745.70 per mechanical hp |
| Shaft | SHP | Propeller shaft (marine/aviation) | 745.70 per mechanical hp |
| Wheel | WHP | At wheels, after drivetrain losses | 745.70 per mechanical hp |
Brake, indicated, shaft and wheel horsepower describe different power quantities or measurement locations. When expressed in mechanical hp, each uses the same watt conversion; the measured power can differ. IHP is derived from cylinder-pressure work before mechanical losses.
Electric Motors vs. Combustion Engines
The shaft-power relationship applies to both electric motors and combustion engines. Some controlled electric drives provide substantial torque from very low speed through a base-speed region. Available torque depends on motor design, control and operating limits; consult the manufacturer’s torque-speed curve. At zero shaft speed, mechanical output power is zero even when torque is nonzero. Rated power alone does not determine vehicle acceleration.
Drivetrain Losses: BHP vs. WHP
Wheel power differs from engine output because of drivetrain losses. The relationship depends on the vehicle, speed, torque, operating conditions and measurement method. A chassis dynamometer measures wheel power; do not apply a universal loss percentage to convert an engine rating into wheel power.
Frequently Asked Questions
What is horsepower?
Mechanical horsepower is a power unit equal to 33,000 ft·lbf/min, approximately 745.6999 W.
How does torque differ from horsepower?
Torque is the moment of a force, expressed here in lbf·ft or N·m. Shaft power is torque times angular speed. Different torque and RPM combinations can therefore produce the same power.
Why do torque and HP cross at 5252 RPM?
For positive torque, mechanical hp and lbf·ft have equal numerical values near 5252.11 RPM. A visible chart crossover also requires the same numerical vertical scale and an operating point at that speed.
BHP vs. WHP vs. PS?
BHP describes brake output power; WHP describes wheel power after drivetrain losses. Both can be expressed in mechanical hp. PS is a distinct metric horsepower unit of approximately 735.4988 W; this calculator uses mechanical hp.
Works for electric motors?
Yes. Mechanical shaft power is torque times angular speed. Motor output ratings can use mechanical hp; an electrically driven motor does not automatically require the separate 746 W electrical-horsepower definition. This calculator does not estimate electrical input power or efficiency.
HP to kW conversion?
Approximately, mechanical hp × 0.7456999 = kW and kW × 1.3410221 = mechanical hp. Metric PS uses a different factor: PS × 0.7354988 ≈ kW. The calculator keeps the mechanical-horsepower definition consistent.
