Enter the SFM (surface feet per minute) and the diameter into the calculator to determine the lathe RPM.

Lathe RPM Formula

The following equation is used to calculate the Lathe RPM.

LRPM = SFM/D * 3.82

  • Where LRPM is the lathe rotations per minute
  • SFM is the surface feet per minute
  • D is the diameter of the tool (in)

To calculate the lathe RPM, divide the surface feet per minute by the diameter of the tool in inches.

What is a Lathe RPM?


A lathe RPM is defined as the rotation speed at which a lathe machine is turning. The correct lathe RPM depends on the size of the tool, the material being cut, and the operation being performed.

How to Calculate Lathe RPM?

Example Problem:

The following example outlines the steps and information needed to calculate Lathe RPM.

First, determine the SFM of the lathe. In this example, the surface feet per minute is given as 4,000.

Next, determine the diameter of the tool. In this example, the diameter is 10 inches.

Finally, calculate the Lathe RPM using the formula above:

LRPM = SFM/D * 3.82

LRPM = 4,000/10 * 3.82

LRPM = 1528 RPM