Calculate RPM, IPM, SFM, IPT and more.

Below are variable abbreviations and formulas for many common milling operations.

Click here to download a printable PDF file containing these formulas.

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Variables / Abbreviations

  • Speed – Surface Feet per Minute (SFM)
  • Feed – Inches per Minute (IPM)
  • Feed per Tooth (FPT)
  • Adjusted Feed per Tooth – Chip Thinning (AFPT)
  • Feed per Revolution (FPR)
  • Depth of Cut (DOC)
  • Width of Cut (WOC)
  • Tool Diameter (D)
  • # of Teeth in Cutter (Z)
  • Metal Removal Rate – Cubic Inches per Minute (MRR)


Milling Formulas

  • Speed (RPM) = (SFM x 3.82) / D
  • Feed (IPM) = RPM x FPT x Z
  • SFM (Surface Feet per Minute) = (RPM x D) / 3.82
  • IPT (Inches per Tooth) = (IPM / RPM) / Z
  • MRR (Cubic Inches per Minute) = IPM * WOC * DOC
  • AFPT (@ less than 1/2 dia. WOC) = IPM x sqroot of (D / WOC)
  • HP (Horsepower Consumption) = MRR x mf
    • mf - steel = 1
    • mf - gray iron = .65
    • mf - aluminum = .3
    • * - 1.5% from total for every degree positive


For lead angle (chip thinning) and effective cutting diameter compensation, see corresponding tool reference page / catalog.