Speed and Feed Calculator

Surface Feet Per Minute (SFM)

SFM Calculator

Surface Feet Per Minute (SFM) Calculator

The SFM calculation for Metric: π×Diameter (mm)×Spindle Speed (RPM)


The SFM calculation for Inch: π×Diameter (inches)×Spindle Speed (RPM)​


Surface Feet Per Minute (SFM) Calculator

Surface Feet Per Minute (SFM) is a measure of the speed at which the surface of a rotating object (like a cutting tool or workpiece) moves relative to its axis. This is a crucial parameter in machining operations, as it helps determine the appropriate cutting speed for various materials and tools, ensuring optimal performance and tool life.

Understanding SFM

SFM is used to standardize the speed of the cutting tool or the workpiece surface. It allows machinists to calculate the ideal cutting speed based on the diameter of the tool or workpiece and the rotational speed (RPM – Revolutions Per Minute). The formula for calculating SFM is:

SFM = (π × Diameter × RPM) / 12


  • π (pi) is a mathematical constant approximately equal to 3.14159.
  • Diameter is the diameter of the workpiece or the cutting tool in inches.
  • RPM is the rotational speed in revolutions per minute.

Why SFM is Important

  • Tool Life: Using the correct SFM helps prevent excessive wear and tear on cutting tools.
  • Surface Finish: The appropriate SFM ensures a good surface finish on the machined part.
  • Efficiency: Optimizing SFM can reduce machining time and improve productivity.
  • Safety: Proper SFM reduces the risk of tool breakage and accidents.

Example Calculation

Suppose you have a tool with a diameter of 2 inches and you want to calculate the SFM at 500 RPM:

SFM = (3.14159 × 2 × 500) / 12 ≈ 261.8 feet per minute

Using an SFM Calculator

An SFM calculator simplifies this process. Here’s how to use it:

  1. Input the Diameter: Enter the diameter of the tool or workpiece.
  2. Input the RPM: Enter the rotational speed.
  3. Calculate: The calculator will automatically compute the SFM using the formula mentioned above.

Practical Applications

  • Machining Operations: Determine the best cutting speeds for operations like milling, turning, and drilling.
  • Material Selection: Different materials require different SFMs for optimal cutting.
  • Tool Selection: Choose the appropriate tools based on the required SFM for a given material and operation.


Understanding and utilizing SFM is critical in machining to ensure efficiency, safety, and quality. By using an SFM calculator, machinists can quickly and accurately determine the optimal cutting speeds for various applications.

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