Unit system
Resulting RPM
Enter values to calculate.
Formula used
RPM = (SFM × 3.82) / D [in]
Indicative value. Adjust based on tool manufacturer recommendations and actual cutting conditions.
How does the formula work?
Imperial system
RPM = (SFM × 3.82) / D [in]
The constant 3.82 comes from 12/π. It converts linear distance (surface feet per minute) to angular velocity (revolutions per minute) based on the tool's circumference.
Metric system
RPM = (m/min × 318.31) / D [mm]
The constant 318.31 comes from 1000/π. It converts m/min to RPM considering the diameter in millimeters.
This calculator converts units geometrically. Recommended cutting speed ranges by material (e.g. 'steel 1045: 80–120 m/min') are empirical data from manufacturers and will be covered in a separate section.