Calculate milling feed rate, spindle speed, or chip load per tooth from RPM, cutting speed, tool diameter, and flute count in in/min or mm/min.
Feed Rate Formula
The calculator uses three formulas depending on which mode you choose.
Feed from RPM:
F = RPM * CL * N
Feed from cutting speed (SFM):
RPM = (SFM * 12) / (pi * D) F = RPM * CL * N
Chip load:
CL = F / (RPM * N)
- F = feed rate (in/min or mm/min)
- RPM = spindle speed (revolutions per minute)
- CL = chip load per tooth (in/tooth or mm/tooth)
- N = number of flutes (teeth)
- SFM = surface feet per minute (cutting speed)
- D = tool diameter (inches)
Assumptions: the formulas assume a single contact point per flute per revolution and consistent units. If you input metric values, the calculator converts internally to inches, runs the math, and converts the output back. The 12 in the SFM formula converts feet to inches. Use m/min × 3.281 to get SFM if your tooling chart is metric.
The three modes match the three unknowns you typically face. "Feed from RPM" is the direct multiplication when you already set spindle speed on the machine. "Feed from SFM" first solves RPM from the recommended cutting speed and tool diameter, then computes feed. "Chip load" reverses the feed equation when you want to verify the per-tooth engagement of a program already running.
Reference Tables
Typical chip load per tooth for a 1/2 inch end mill in common materials. Scale roughly with diameter (smaller tools take lighter chips).
| Material | Chip load (in/tooth) | Chip load (mm/tooth) |
|---|---|---|
| Aluminum | 0.005 - 0.010 | 0.13 - 0.25 |
| Brass | 0.004 - 0.008 | 0.10 - 0.20 |
| Mild steel | 0.002 - 0.005 | 0.05 - 0.13 |
| Stainless steel | 0.001 - 0.004 | 0.03 - 0.10 |
| Titanium | 0.001 - 0.003 | 0.03 - 0.08 |
| Hardwood | 0.008 - 0.015 | 0.20 - 0.38 |
| Plastic | 0.005 - 0.012 | 0.13 - 0.30 |
Typical cutting speed (SFM) for carbide tooling.
| Material | Carbide SFM | HSS SFM |
|---|---|---|
| Aluminum | 600 - 1200 | 250 - 400 |
| Brass | 300 - 700 | 150 - 300 |
| Mild steel | 300 - 500 | 80 - 120 |
| Stainless steel | 150 - 350 | 40 - 80 |
| Titanium | 100 - 250 | 30 - 60 |
| Cast iron | 250 - 450 | 60 - 100 |
Worked Examples and FAQ
Example 1: Feed from RPM. A 4 flute end mill at 3500 RPM with a 0.002 in/tooth chip load.
F = 3500 × 0.002 × 4 = 28 in/min.
Example 2: Feed from SFM. A 0.5 in carbide end mill in aluminum at 800 SFM, 3 flutes, 0.005 in/tooth.
RPM = (800 × 12) / (π × 0.5) = 6112 RPM. F = 6112 × 0.005 × 3 = 91.7 in/min.
Example 3: Chip load check. Program runs at 40 in/min, 5000 RPM, 2 flutes.
CL = 40 / (5000 × 2) = 0.004 in/tooth.
What if my chip load is too low? Rubbing instead of cutting. The tool generates heat and dulls fast. Increase feed or reduce RPM.
What if it is too high? Tool deflection, broken edges, or stalled spindle. Drop the feed or add flutes.
Do I scale chip load with tool diameter? Yes. The values in the table are for roughly 1/2 in tools. For a 1/8 in tool, use about a quarter of the listed chip load. For a 1 in tool, you can run at the upper end or beyond.
Does flute count change feed? Yes, directly. Doubling flutes at the same RPM and chip load doubles the feed rate. That is why 3 flute and 4 flute end mills feed faster than 2 flute at the same per-tooth load.
Why is the SFM formula 12 / π and not something simpler? SFM is feet per minute at the cutting edge. Diameter is in inches. The 12 converts feet to inches and π converts a circumference to a diameter so you can solve for RPM.
