HP to Torque Calculator
Evaluate mechanical torque (lb-ft or Nm) from motor horsepower (HP) and rotational speed (RPM), or convert twisting metrics back to mechanical horsepower capacities. Settle shaft lines dynamically.
HP to Torque Converter
How to Use the HP to Torque Calculator
Converting motor output power in horsepower (HP) to equivalent shaft twisting force in torque is direct. Follow these steps:
- 1Enter Horsepower: Input the mechanical horsepower rating (HP).
- 2Enter Rotational Speed: Input the rotational speed of the shaft in revolutions per minute (RPM).
- 3Select Result Unit: Choose between imperial Pound-feet (lb-ft) and metric Newton-meters (Nm).
- 4Calculate: Click the "Calculate to Torque" button to run the conversion.
How to Convert HP to Torque
In mechanical design, horsepower (HP) represents the rate of doing work over time (power), whereas torque represents the physical rotational twisting force generated on a drive shaft. You cannot convert horsepower directly to torque without knowing the shaft speed in revolutions per minute (RPM). At a constant power rating, torque is inversely proportional to RPM; a slower rotating shaft delivers significantly higher torque than a fast rotating shaft. In the imperial system, the relationship uses the constant 5252, which is the RPM where torque in lb-ft and power in HP are mathematically equal. In the metric system, the constant 7121 relates horsepower to Newton-meters.
Real-Life Sizing Scenarios
Scenario 1: Sizing Torque in lb-ft for a 10 HP Motor
An electrical contractor calculates the torque output of a 10 HP industrial electric motor rotating at a standard speed of 1800 RPM:
Torque (lb-ft) = (10 HP × 5252) ÷ 1800 RPM = 29.18 lb-ft
Scenario 2: Sizing Torque in Nm for a 220 HP Motor
A mechanical designer checks the torque generated by a 220 HP industrial pump motor spinning at 3000 RPM:
Torque (Nm) = (220 HP × 7121) ÷ 3000 RPM = 522.21 Nm
Step-by-Step Manual Sizing Guide
- 1Identify system parameters: Settle the mechanical horsepower output (HP) and shaft speed (RPM).
- 2Select the correct formula: Use
Torque (lb-ft) = (HP × 5252) ÷ RPMfor imperial, orTorque (Nm) = (HP × 7121) ÷ RPMfor metric. - 3Solve the calculation: Multiply horsepower by the chosen constant, and divide the product by the RPM to locate torque.
HP to Torque Conversion Chart
The table below displays standard horsepower ratings and their corresponding torque outputs in both pound-feet (lb-ft) and Newton-meters (Nm) at a standard rotational speed of 1800 RPM:
| Power (HP) | Rotational Speed (RPM) | Torque (lb-ft at 1800 RPM) | Torque (Nm at 1800 RPM) |
|---|---|---|---|
| 1.0 HP | 1800 RPM | 2.92 lb-ft | 3.96 Nm |
| 5.0 HP | 1800 RPM | 14.59 lb-ft | 19.78 Nm |
| 10.0 HP | 1800 RPM | 29.18 lb-ft | 39.56 Nm |
| 20.0 HP | 1800 RPM | 58.36 lb-ft | 79.12 Nm |
| 50.0 HP | 1800 RPM | 145.89 lb-ft | 197.81 Nm |
| 75.0 HP | 1800 RPM | 218.83 lb-ft | 296.71 Nm |
| 100.0 HP | 1800 RPM | 291.78 lb-ft | 395.61 Nm |
| 200.0 HP | 1800 RPM | 583.56 lb-ft | 791.22 Nm |
HP to Torque Electric Motor
Electric motors exhibit full starting torque immediately upon voltage application, unlike combustion engines. Converting active running horsepower to full load torque determines coupling and drive chain requirements:
Torque (lb-ft) = (HP × 5252) ÷ RPM
250 Nm Torque to HP
Converting a torque value of 250 Nm back to equivalent horsepower at a rotational speed of 3000 RPM:
Horsepower = (250 Nm × 3000 RPM) ÷ 7121 = 105.32 HP
Torque Nm to HP Formula
The standard thermodynamic equation rearranged to solve for mechanical horsepower when torque is in Newton-meters:
HP = (Torque_Nm × RPM) ÷ 7121
Frequently Asked Questions (FAQs)
To convert horsepower (HP) to torque, multiply the HP rating by the standard constant 5252 (for torque in lb-ft) or 7121 (for torque in Nm), and then divide the product by the shaft speed in RPM: Torque (lb-ft) = (HP × 5252) ÷ RPM.
To calculate horsepower from engine torque, multiply the torque value by the engine speed in RPM and divide by the corresponding unit constant: HP = (Torque_lb-ft × RPM) ÷ 5252 or HP = (Torque_Nm × RPM) ÷ 7121.
One mechanical horsepower (HP) is equal to 745.7 Watts of electrical power, or 550 foot-pounds of work per second (which equates to 33,000 foot-pounds per minute). It is the historical measure established by James Watt to compare steam output to working draft horses.
A 1/4 HP motor develops approximately 186.4 Watts of continuous mechanical output. At a standard speed of 1725 RPM, it produces about 0.76 lb-ft (1.03 Nm) of continuous running torque, which is standard for small workshop appliances like drill presses and fans.
A 1/3 HP motor is stronger than a 1/4 HP motor. One-third horsepower yields about 248.7 Watts of active power output, whereas one-quarter horsepower yields only 186.4 Watts. A 1/3 HP motor can support roughly 33% more load at the same operational speed.
A 1 HP motor can lift 550 pounds by one foot in exactly one second (or 33,000 pounds by one foot in one minute). The actual weight capacity can be increased to any level using gear reduction systems, which reduce shaft RPM to multiply the torque output.