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Feeds & speeds

Spindle Speed and Cutting Speed Calculator

Convert between spindle speed and surface cutting speed at the effective tool or workpiece diameter. Use it for milling, drilling, or turning setup checks.

LOCAL CALC / SPINDLE
NO DATA SENT

INPUT

Enter values

Use effective cutting diameter.

OUTPUT

READY

Enter known values and calculate.

Results stay on this device.
Shop-floor check

RPM is a mathematical starting point, not a safe operating guarantee. Verify the cutter, holder, workholding, balance, machine speed limit, material, and setup before running.

01 / METHOD

How to use this calculator

  1. Choose metric or inch units.
  2. Choose whether to solve for RPM or cutting speed.
  3. Enter the effective cutting diameter and known value, then calculate.

02 / APPLICATION

Where it helps

  • Setting a starting spindle speed from tooling data
  • Checking surface speed at a machine RPM limit
  • Comparing metric and inch shop data

03 / BOUNDARIES

Assumptions and limitations

Assumes

  • Constant diameter at the cutting point
  • Entered cutting speed matches the selected unit system
  • No compensation for interrupted cuts or machine dynamics

Does not cover

  • Turning diameter changes during facing
  • Small drills may be limited by spindle capability
  • Tool maker recommendations and machine limits take priority

04 / QUESTIONS

Frequently asked questions

What diameter should I use?

Use the effective diameter at the cutting edge. For turning, this is the current work diameter; for a standard end mill, it is normally cutter diameter.

Should calculated RPM be rounded?

Yes. Use a speed the machine can command, generally rounding down when power, rigidity, heat, workholding, or tool limits are uncertain.

Is SFM the same as feet per minute feed?

No. SFM is surface cutting speed at the circumference. Feed rate is linear tool motion, usually inches or millimetres per minute.