Mill Feed Rate Calculator
Feed rate on a milling machine is the linear speed at which the cutter advances into the work, usually expressed in inches per minute (IPM) or millimeters per minute (mm/min). It depends on spindle RPM, flute count, and the chip load each tooth is supposed to take. This mill feed rate calculator takes those inputs, applies a chip-thinning correction when radial width is less than half the tool diameter, and returns IPM, IPT, IPR, and metric feed rate in one step.
The mill feed rate formula
Feed rate on an end mill is:
Feed rate (IPM) = RPM x chip load per tooth x number of flutes
Example: a 4-flute end mill spinning 3,056 RPM in mild steel with a 0.002 inch chip load runs at 3,056 x 0.002 x 4 = 24.4 IPM. That result is the feed value programmed into a G-code F word.
Chip load per tooth by material
| Material | Baseline IPT (0.5 in D) |
|---|---|
| Aluminum | 0.004 |
| Mild steel (1018) | 0.002 |
| Alloy steel (4140) | 0.0015 |
| Stainless 304 | 0.0015 |
| Tool steel | 0.001 |
| Cast iron | 0.003 |
| Brass | 0.003 |
| Titanium Ti-6Al-4V | 0.001 |
| Inconel 718 | 0.0008 |
| Plastic (Delrin) | 0.005 |
These are a 1/2 inch end mill baseline. Scale down 25-50 percent for tools 1/8 inch and smaller; scale up 25 percent for tools 3/4 inch and larger.
Chip thinning and radial engagement
When the radial width of cut (Ae) is less than half the tool diameter, the chip each tooth sees is thinner than the programmed IPT because the tooth only contacts the work across a shallow arc. The Sandvik chip-thinning correction scales IPT up by D / (2 x sqrt(Ae x (D - Ae))). At Ae = 0.05 inch on a 0.5 inch end mill (10 percent radial) the factor is 1.67x, meaning feed rate can be 67 percent higher than the naive calculation and still keep chip thickness at the cutter target.
Imperial and metric feed rate
This calculator returns feed rate in both IPM and mm/min. A quick conversion: mm/min = IPM x 25.4. Controls from Haas, Fanuc, Heidenhain, and Siemens all accept either unit depending on how the post is configured. When in doubt, program in the same units the drawing calls out; imperial drawings use IPM, metric drawings use mm/min.