CNC Feed Rate Calculator
A CNC feed rate calculator turns spindle RPM, chip load per tooth, and flute count into the feed rate a CNC control needs. Output is given in both IPM (imperial, most Haas and Fadal controls) and mm/min (metric, most DMG Mori and Mazak controls), so the same numbers work on any machine. Chip load defaults scale with tool diameter and match the values in Harvey Tool, Helical, and Sandvik data books.
CNC feed rate formula
The CNC feed rate equation is the same whether you program a VMC, a CNC router, or a high-speed lathe:
- Feed rate (IPM) = RPM x chip load per tooth x number of flutes.
- Metric: Feed rate (mm/min) = IPM x 25.4.
- For compute mode: RPM = (SFM x 12) / (pi x D).
Example: 1/4 inch 2-flute carbide end mill in 6061 aluminum. SFM target = 1500. RPM = (1500 x 12) / (pi x 0.25) = 22,918 RPM. Chip load = 0.003 IPT (0.004 baseline scaled 0.75 for 1/4 inch tool). Feed rate = 22,918 x 0.003 x 2 = 137.5 IPM = 3,492 mm/min. If the CNC maxes at 12,000 RPM, cap there and recompute feed: 12,000 x 0.003 x 2 = 72 IPM.
CNC feed rate calculator metric support
A CNC feed rate calculator metric workflow is identical to imperial once tool diameter is set in mm. RPM calculation is unit-independent. Feed rate in mm/min equals IPM x 25.4. For European CNCs running Siemens 840D or Heidenhain TNC7, the mm/min output goes straight into the F word of your G-code. A Haas, Fanuc, or Mazak control accepts either IPM (G94/G95 inch mode) or mm/min (G21 metric mode). This calculator returns both.
Chip load per tooth by material
| Material | Chip load (IPT) |
|---|---|
| Aluminum 6061 | 0.004 |
| Mild steel (1018) | 0.002 |
| Alloy steel (4140) | 0.0015 |
| Stainless steel | 0.0015 |
| Titanium Ti-6Al-4V | 0.001 |
| Brass | 0.003 |
| Hardwood | 0.008 |
| Softwood | 0.012 |
| MDF | 0.010 |
| Plywood | 0.009 |
| Plastic (Delrin, acrylic) | 0.005 |
Small-tool chip load scaling
A 1/16 inch end mill cannot take the full chip load a 1 inch end mill can. The flute is smaller, the cutter is less rigid, and cutting force matters more per unit of tool stiffness. This CNC feed rate calculator scales chip load to 50 percent under 1/8 inch, 75 percent for 1/8-1/4 inch, and 125 percent over 3/4 inch. Override the auto-scaling with the chip load override field if you have vendor-specific data.
Feed rate vs spindle RPM
Spindle RPM comes from the cutting speed (SFM), which depends on material and tool material. Feed rate comes from RPM times chip load times flutes. Changing chip load does not change RPM; changing SFM does not change chip load. They are independent inputs the CNC program sees as two separate words (S for spindle, F for feed). A CNC feed rate calculator helps you set F without touching S.