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    Feeds & Speeds

    SFM to RPM Conversion

    Convert surface feet per minute to spindle RPM for a given cutter diameter.

    milling
    turning
    feeds-speeds
    formula
    beginner

    Formula

    RPM = (3.82 × SFM) / D_inches

    Units: inch

    Machine-readable reference

    Structured metadata for formulas, tags, canonical status, and future diagram support.

    Slug

    sfm-to-rpm

    Category

    Feeds & Speeds

    Canonical

    Yes

    Updated

    4/23/2026

    Units

    inch

    Tags

    milling, turning, feeds-speeds, formula

    Source

    Machinery's Handbook, 31st ed., Speeds and Feeds

    SFM to RPM

    Surface speed is the linear speed at the cutting edge. Spindle speed depends on tool or workpiece diameter.

    Core formula

    RPM = (3.82 × SFM) / D_inches

    Practical use

    • Pick SFM from the material chart.
    • Plug in the cutter diameter.
    • Round to the nearest safe spindle speed.

    Example

    4140 steel, 0.500 in end mill, 100 SFM: RPM = (3.82 × 100) / 0.500 = 764 RPM

    Source: Machinery's Handbook, 31st ed., Speeds and Feeds