Speeds and Feeds Calculator —
RPM and Feed Rate for Milling and Turning
The Two Formulas
Spindle speed. RPM = (12 × SFM) / (π × D), where SFM is surface feet per minute and D is the diameter in inches. The shop shortcut RPM ≈ (3.82 × SFM) / D is the same equation with the constants folded together. For milling and drilling, D is the tool diameter; for turning, D is the workpiece diameter at the cut, which is why a facing cut to center wants constant surface speed rather than a fixed RPM.[1]
Feed rate. Feed (in/min) = RPM × number of flutes × chip load per tooth. Chip load is the thickness of material each cutting edge removes per revolution, and it is the number that actually protects your tool: too low and the edge rubs and work hardens the material (especially in stainless and superalloys), too high and the edge chips. For turning, set flutes to 1 and read chip load as feed per revolution.[1]
SFM Starting Points by Material
Published ranges vary by source, coating, and operation; these are conservative milling ranges for uncoated to TiAlN-coated tooling, consistent with the values in our Machining Inconel guide. The calculator preset is a midpoint of each range.[1][2]
| Material | HSS (SFM) | Carbide (SFM) | Calculator preset (HSS / carbide) |
|---|---|---|---|
| Aluminum 6061 / 7075 | 200–400 | 600–1500 | 250 / 800 |
| Brass 360 | 150–300 | 400–1000 | 200 / 500 |
| Mild steel (1018, A36) | 70–110 | 250–450 | 90 / 350 |
| 4140 / 4340 pre-hard (28–32 HRC) | 40–80 | 200–350 | 60 / 250 |
| Stainless 304 / 316 | 40–70 | 200–400 | 50 / 300 |
| 17-4 PH (aged) | 30–60 | 150–300 | 40 / 200 |
| Titanium Ti-6Al-4V | 20–40 | 100–250 | 30 / 150 |
| Inconel 718 (annealed) | 10–20 | 80–150 | 15 / 100 |
| Inconel 718 (aged) | not recommended | 30–80 | — / 50 |
| Delrin / UHMW | 300–600 | 500–1500 | 400 / 600 |
Chip Load Starting Points
Chip load scales with tool diameter because a bigger core can take a bigger bite. These are conservative per-tooth values for side milling at moderate depth; the calculator picks the column nearest your entered diameter.[1]
| Material family | 1/8" end mill | 1/4" end mill | 1/2" end mill | 1" end mill |
|---|---|---|---|---|
| Aluminum, brass | 0.001 | 0.002 | 0.004 | 0.006 |
| Carbon & alloy steel | 0.0005 | 0.001 | 0.002 | 0.004 |
| Stainless & titanium | 0.0004 | 0.0008 | 0.0015 | 0.003 |
| Nickel superalloys | 0.0003 | 0.0006 | 0.001 | 0.002 |
| Plastics (Delrin, UHMW) | 0.002 | 0.004 | 0.006 | 0.010 |
We run these numbers daily
From 6061 fixtures to aged Inconel flight hardware, C&W machines the full range of these materials under an AS9100D quality system.