Feed & Speed Calculator
The whole calculation in one pass: cutting speed and tool diameter give you spindle RPM, then chip load and flute count give you the table feed to program — no bouncing between two calculators.
Starting points for cutting speed and chip load
| Material | SFM (carbide) | Chip load, 1/2" 4-flute (in) |
|---|---|---|
| Aluminum (free machining) | 800–2000 | 0.004–0.008 |
| Mild steel (1018) | 350–550 | 0.003–0.005 |
| Alloy steel (4140) | 250–400 | 0.002–0.004 |
| Stainless steel (304) | 200–350 | 0.002–0.004 |
| Cast iron (gray) | 300–500 | 0.003–0.006 |
| Titanium (Ti-6Al-4V) | 100–180 | 0.001–0.003 |
Starting points for a 1/2" 4-flute carbide end mill — scale chip load roughly with tool diameter, and confirm against your tool manufacturer's data sheet before running it.
Why this is a two-step calculation, not one
Cutting speed (SFM) and chip load are independent decisions — one is about how fast the edge should move through the material, the other is about how much material each tooth should bite off per revolution. RPM converts the first into a spindle number: RPM = (SFM × 12) ÷ (π × diameter). Feed rate converts the second into a table number: IPM = RPM × chip load × flute count. Running both through one page means you only have to reason about SFM and chip load once, and the RPM used for the feed calculation is guaranteed to match the RPM you're actually about to dial in.
Chip load is not "one number" for a tool
The right chip load depends on tool diameter, flute count, material, and how rigid the setup is — a 1/8" end mill and a 1" end mill in the same material do not want the same IPT, because a bigger flute can physically carry a bigger, stronger chip. The table above is scaled for a 1/2" 4-flute tool as a reference point; scale it down for smaller tools and up (cautiously) for bigger ones, and always start conservative on a new setup.
When the math and the machine disagree
If the calculated feed rate sounds too aggressive for your machine, spindle, or fixturing, trust your judgment over the number — these formulas assume the tool can actually take the chip load you specify. Chatter, poor finish, or a spindle straining to hold RPM under load are all signs to back off chip load or SFM before you break a tool or scrap a part.