CNC Cutting Speed & RPM Calculator
Convert cutting speed and diameter into spindle RPM, or reverse it.
Results
Spindle speed
- Cutting speed
- 100 m/min328.08 SFM
- Use a known cutting speed from tool data or your process. Verify machine and tooling RPM limits separately.
This calculator converts a known cutting speed; it does not recommend a machining speed. Check tool, holder, workpiece and machine RPM limits separately. The initial values are arithmetic examples, not operating recommendations. Turning with a changing diameter also changes cutting speed at fixed RPM.
Formula · How it works
Formula
n = 1000Vc / (πD) [D: mm, Vc: m/min]Vc = πDn / 1000 [D: mm, Vc: m/min]Metric: Vc (m/min) = π × D (mm) × n / 1000, and n = 1000Vc/(πD). Imperial: Vc (SFM) = π × D (in) × n / 12, and n = 12Vc/(πD). Internally, diameter is converted to m and speed to m/s; n remains rev/min.
Worked example
A 10 mm tool at 100 m/min requires n = 1000 × 100 / (π × 10) ≈ 3,183.10 rpm. The same cutting speed is approximately 328.08 SFM. Entering that RPM and diameter returns 100 m/min.
How it works
Cutting speed is the tangential speed at the cutting diameter. A smaller diameter requires more RPM to achieve the same cutting speed. This relationship applies to both milling tools and rotating workpieces.
Common questions
Does the calculator recommend cutting speeds for materials?
No. Enter a cutting speed from the tool manufacturer's data or a validated process. Material, tool grade, coating, coolant and machining conditions affect the appropriate value.
What is SFM?
SFM means surface feet per minute. It measures cutting speed in feet per minute; 1 m/min equals approximately 3.28084 SFM.
Which diameter should I use for turning?
Use the workpiece diameter at the cut. For milling, use the effective cutting diameter of the tool. At a fixed RPM, changing the cutting diameter changes surface speed.