MachiningCalc / Spindle Speed Calculator

Spindle · surface speed

Spindle Speed Calculator

Convert between surface speed and spindle RPM using the actual cutting diameter. Useful for milling, drilling and turning setup.

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Calculator

Enter your known cutting data. Results update automatically.

Result—
Input reference—

Use manufacturer cutting data and stay within machine, tool and workholding limits.

Calculation check: This is the same reversible SFM/RPM geometry used on the main calculator, with the cutting diameter as the link between linear and rotational speed.
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US unitsInches, SFM, RPM, IPM
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Connected workflowLinks to the next calculation

Calculation method

How this calculator works

RPM = SFM × 12 ÷ (π × Diameter)SFM = π × Diameter × RPM ÷ 12

Values are deterministic outputs from the inputs shown above; cutting recommendations are not inferred.

Spindle speed versus surface speed

RPM tells you how fast the spindle rotates. SFM describes the linear speed at the cutting circumference. Diameter connects the two values.

Machine RPM limits

The mathematical RPM can exceed a machine's maximum speed, particularly with small tools. Cap settings to the machine and workholding limits and recalculate the achieved surface speed if needed.

Technical references