Enter the rotational speed and power at the same operating point into the calculator to determine the corresponding torque. Note: peak/maximum torque generally cannot be found from “maximum RPM” and “maximum horsepower” alone unless you also know the RPM at which that horsepower is produced (i.e., a point on the torque curve).

Torque Calculator

Power, Speed & Torque
Force & Radius
Shaft Size

Enter any 2 values to calculate the missing variable (values must correspond to the same operating point).

Torque from Horsepower and RPM Formula

The following formula is used to calculate torque at the RPM where the stated power applies. For example, if you use peak horsepower and the RPM at which peak horsepower occurs, the result is torque at peak horsepower (not necessarily maximum/peak torque).

T = (5252 × HP) / RPM
  • Where T is the torque at that operating point (lb-ft)
  • RPM is the rotational speed at that same operating point (rev/min)
  • HP is the power at that same operating point (mechanical horsepower)

To calculate torque in lb-ft, multiply horsepower by 5252 (a rounded constant) and divide by RPM. (An SI equivalent is T (N·m) ≈ 9550 × P(kW) / RPM.)

How to Calculate Torque from Horsepower and RPM?

The following two example problems outline how to calculate torque from power and rotational speed (all values must be from the same operating point).

Example Problem #1:

  1. First, determine the rotational speed (RPM) at the operating point of interest. In this example, the rotational speed is 40 RPM.
  2. Next, determine the power (hp) at that same speed. For this problem, the power is 30 hp.
  3. Finally, calculate the torque using the formula above: 

T = (5252 × HP) / RPM

Inserting the values from above and solving the equation with the input values gives: 

T = 5252 × 30 / 40 = 3939 (lb-ft)

Example Problem #2: 

Using the same process as example problem 1, we first define the variables outlined by the formula. In this case, the values are:

rotational speed (RPM) = 15

power (hp) = 29

Entering these values yields:

T = 5252 × 29 / 15 = 10153.866 (lb-ft)