Horsepower to RPM Calculator | Calculate RPM from HP & Torque

Horsepower to RPM Formula: Calculate RPM from HP & Torque

The formula to calculate RPM based on horsepower and torque is:

Where:

=Revolutions per minute
=A unit of power (HP, Watts, or Kilowatts)
=Rotational force (measured in pound-foot, Newton-meter, etc.)
=A constant derived from the conversion of power and torque units

Why 5252?

The constant 5252 comes from unit conversion, ensuring that power (in horsepower), torque (in pound-foot), and rotational speed (in RPM) are mathematically consistent.

Key Features: Unit Flexibility for Metric & Imperial Systems

Our calculator allows you to seamlessly compute RPM with various input units, supporting:

Power Units

Horsepower (HP)
Watts (W)
Kilowatts (kW)

Torque Units

Pound-inch (lb-in)
Pound-foot (lb-ft)
Newton-meter (Nm)
Newton-centimeter (Ncm)
Gram-meter (g·m)
Kilogram-centimeter (kg·cm)
Kilogram-meter (kg·m)

How to Use the Calculator

Select Power Value: Enter the power of your engine or motor and choose its unit (HP, Watts, or Kilowatts).
Enter Torque Value: Specify the torque applied, along with the unit (e.g., pound-foot or Newton-meter).
Calculate RPM: Click "Calculate" to instantly obtain the RPM.

Horsepower to RPM Calculation Examples

Metric Example

A motor produces 15 kW of power and has a torque of 50 Nm.

Convert power to HP:

Calculate RPM:

Imperial Example

An engine delivers 300 HP and a torque of 400 lb-ft.

Calculate RPM:

Frequently Asked Questions

1. How do you calculate horsepower from torque and RPM?

To find horsepower:

This relationship demonstrates that horsepower depends on both torque and rotational speed.

2. How do you convert torque to horsepower?

If you know the engine’s RPM:

3. Why do torque and horsepower curves intersect at 5252 RPM?

At 5252 RPM, the conversion factor aligns torque and horsepower. This is because 5252 is derived from:

where 33,000 is the work done in foot-pounds per minute by one horsepower, and 2π represents one revolution.

Conclusion

The relationship between horsepower, torque, and RPM is essential for understanding the performance of engines and motors. Our Horsepower to RPM Calculator makes it easy to calculate RPM by supporting various power and torque units.

Whether you're working with metric or imperial systems, this tool simplifies complex calculations and improves productivity.