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Milling Speeds and Feeds
Guide · Updated October 27, 2026
Milling speeds and feeds come down to two choices: a surface speed that suits the tool and material, and a chip load each tooth can handle. Everything else is arithmetic. Here are conservative starting values for end mills, and worked inch and metric examples.
Skip the arithmetic
The free speeds and feeds calculator turns SFM or m/min into RPM. For precision setups, the Gage Block Calculator builds any stack. Free, no login.
Formulas
- RPM: SFM × 3.82 ÷ D (in), or 1000 × Vc ÷ (π × D) (mm)
- Feed: IPM = RPM × flutes × chip load, or mm/min = RPM × z × fz
Conservative starting values (carbide end mills)
| Material | SFM | Chip load, 1/2 in tool |
|---|---|---|
| Aluminum (6061) | 600–1000 | 0.003–0.004 in |
| Mild steel | 300–400 | 0.002–0.003 in |
| Stainless (304) | 200–300 | 0.0015–0.0025 in |
Starting points for rigid setups only. HSS runs at about a third of these speeds. Follow the tool maker's data.
Worked examples
- 1/2 in 3-flute carbide, 6061, 800 SFM, 0.003 in/tooth: 800 × 3.82 ÷ 0.5 ≈ 6,112 RPM, so 6,112 × 3 × 0.003 ≈ 55 IPM.
- 1/2 in 4-flute carbide, mild steel, 350 SFM, 0.002 in/tooth: 2,674 RPM, so about 21 IPM.
- 10 mm 4-flute carbide, mild steel, 100 m/min, 0.05 mm/tooth: 1000 × 100 ÷ (π × 10) ≈ 3,183 RPM, so about 637 mm/min.
Step by step
- Pick a surface speed: Choose a conservative SFM or m/min for the tool material and workpiece.
- Work out RPM: RPM = SFM × 3.82 ÷ D, or 1000 × Vc ÷ (π × D).
- Pick a chip load: Start with a conservative chip load per tooth for the tool diameter.
- Work out feed: IPM = RPM × flutes × chip load. Correct for chip thinning at light radial cuts.
- Test and adjust: Run a test cut, watch the chips and listen, then adjust speed first and feed second.
New to this? Start with feeds and speeds basics, then drilling and tapping.
FAQ
How do I calculate milling feed rate?
IPM = RPM × number of flutes × chip load. A 1/2 in 3-flute end mill at 6,112 RPM and 0.003 in per tooth feeds at about 55 IPM.
What chip load should I use for an end mill?
As a conservative start for carbide in aluminum, roughly 0.001 in per tooth for 1/8 in, 0.002 for 1/4 in and 0.003 to 0.004 for 1/2 in. Use less in steel, then follow the tool maker's chart.
What is chip thinning?
At light radial engagement (under half the diameter), the actual chip is thinner than the programmed chip load. Raise the feed to compensate, or the tool rubs and wears.
Should I use climb or conventional milling?
On rigid CNC machines, climb milling usually gives a better finish and tool life. On manual machines with backlash, conventional milling is safer.
Is there a free speeds and feeds calculator?
Yes. The AskMachinist speeds and feeds calculator converts SFM or m/min to RPM, free with no login.
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