SFM Calculator
Calculate surface feet per minute, spindle RPM, or tool diameter for machining and cutting operations using standard imperial formulas.
Enter machining details
Result
Enter the machining values and choose what you want to calculate.
Surface speed
SFM describes how many feet of material pass the cutting edge each minute at the tool or workpiece circumference.
Diameter affects RPM
At the same target SFM, a smaller tool requires a higher RPM while a larger diameter requires a lower RPM.
Start conservatively
Manufacturer charts are a starting point. Reduce speed when machine rigidity, tool holding, or cooling is limited.
Frequently asked questions
What is the formula for SFM?
SFM = π × diameter in inches × RPM ÷ 12. A common shop approximation is diameter × RPM ÷ 3.82.
How do I calculate RPM from SFM?
RPM = SFM × 12 ÷ (π × diameter in inches), or approximately SFM × 3.82 ÷ diameter.
Can I enter diameter in millimetres?
Yes. The calculator converts millimetres to inches before applying the imperial SFM formula.
Is SFM the same as feed rate?
No. SFM is cutting surface speed. Feed rate describes how quickly the cutter advances through the material.
Results are estimates generated locally in your browser from standard geometry, material yield and waste assumptions. They are for planning purposes only, not engineering, structural, code or supplier advice. Confirm dimensions, material strength, delivery constraints and local building codes with a licensed professional before purchasing or building. VisionVix accepts no liability for decisions based on this tool's output.
