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Spindle Speed Calculator

Work out spindle speed instantly with clear inputs, formula shown and shareable results.

About Spindle Speed Calculator

Spindle speed is the cutting speed relation rearranged: rpm = 12 x SFM / (pi x diameter). Handbook cutting speeds are properties of the material and tool pairing, so this is the step that turns a recommendation into a machine setting.

Formula

Spindle speed

rpm = 12 x SFM / (pi x D in)

Worked example

With the default values below, Spindle Speed Calculator returns Spindle speed required of 2,292. Change any input above and every figure here is recalculated in your browser.

Inputs used

Recommended cutting speedminimum 1 SFM
300 SFM
Tool diameterminimum 0.01 in
0.5 in

Results

Spindle speed required
2,292 rpm
Nearest practical setting
2,300 rpm
Cutting speed in metric units
91.44 m/min
Tool circumference
1.571 in

Step by step

  1. 1Values used
  2. 2Spindle speed
  3. 3Spindle speed required= 2,292 rpm
  4. 4Nearest practical setting= 2,300 rpm
  5. 5Cutting speed in metric units= 91.44 m/min
  6. 6Tool circumference= 1.571 in

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Spindle Speed figure worked out?

rpm = 12 x SFM / (pi x D in). Spindle speed is the cutting speed relation rearranged: rpm = 12 x SFM / (pi x diameter).

Should I use the top of the recommended range?

Only on rigid setups with good coolant. Speed drives tool wear far more strongly than feed does, so starting mid-range and increasing while watching the edge is the safer route.

What values do I need to enter?

This calculator takes 2 inputs: Recommended cutting speed, Tool diameter. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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