Convert Surface feet per minute to Spindle RPM — Machining & CNC
Assumptions: Default tool/work diameter = 1.0 in. Formula: RPM = 3.8197 × SFM ÷ D(in).
Formula
RPM = (SFM × 12) ÷ (π × diameter_in) [diameter defaults to 1.0 in]
Why this matters in machining & cnc
Cutting speed (SFM) is a material property; the RPM you dial in depends on tool/part diameter. The UI must expose a diameter field — default here is 1 inch. Smaller diameters need higher RPM for the same SFM.
Surface feet per minute to Spindle RPM reference table (at 1.0 in tool/work diameter)
| Surface feet per minute (SFM) | Spindle RPM (RPM) |
|---|---|
| 50 | 191 |
| 100 | 382 |
| 150 | 573 |
| 200 | 764 |
| 300 | 1,146 |
| 400 | 1,528 |
| 600 | 2,292 |
| 1,000 | 3,820 |