# Feed Speed Calculator

Feed speed calculator for CNC milling. Enter end mill diameter, material, flutes, and get spindle RPM plus feed rate in IPM. Drill speed and feed calculator support built in.

## What this calculates

This feed speed calculator is the fastest way to get spindle RPM and feed rate for an end mill. Pick your tool diameter, material, and flute count, and the calculator runs the two industry-standard equations (SFM to RPM, and chip load to IPM) with baseline values drawn from Machinery's Handbook. Same math a drill speed and feed calculator uses, trimmed for milling.

## Inputs

- **End Mill Diameter** (in) — min 0.001 — End mill cutting diameter.
- **Workpiece Material** — options: Aluminum 6061, Mild / low carbon steel, Alloy steel (4140), Stainless steel (304, 316), Cast iron, Brass, Titanium (Ti-6Al-4V), Plastic (Delrin, UHMW) — Pick the material you are cutting.
- **Tool Material** — options: HSS, Carbide — Carbide runs at 2-3x the SFM of HSS.
- **Flutes** — min 1, max 8 — Number of cutting edges on the end mill. 2 for aluminum, 3-4 for steel.
- **Chip Load Override** (in/tooth) — min 0 — Optional. Override the automatic chip load per tooth (IPT).

## Outputs

- **Spindle Speed** (RPM) — Spindle RPM from (SFM x 12) / (pi x D).
- **Feed Rate** (IPM) — Linear feed rate in inches per minute.
- **Surface Speed** (SFM) — Cutting speed in surface feet per minute.
- **Chip Load** (IPT) — Chip load per tooth used in the feed equation.
- **Feed Rate (metric)** (mm/min) — Feed rate in millimeters per minute.

## Details

The two equations a feed speed calculator runs

Every feed speed calculator boils down to two formulas:

  - RPM = (SFM x 12) / (pi x D) converts a target surface cutting speed (surface feet per minute) into spindle RPM for a given tool diameter D.

  - Feed rate = RPM x chip load x flutes converts that RPM into a linear feed rate in inches per minute.

For a 1/4 inch carbide end mill in aluminum at 1200 SFM: RPM = (1200 x 12) / (pi x 0.25) = 18,335 RPM. At 2 flutes and 0.003 IPT chip load, feed rate = 18,335 x 0.003 x 2 = 110 IPM.

Baseline SFM by material

These are conservative midpoints safe for a general-purpose shop. Production cells with rigid machines and high-pressure coolant can run 20-30 percent faster; hobby machines should back off 20-30 percent.

  - Aluminum: 600 SFM HSS, 1200 SFM carbide

  - Mild steel: 100 SFM HSS, 350 SFM carbide

  - Stainless: 60 SFM HSS, 200 SFM carbide

  - Titanium: 40 SFM HSS, 120 SFM carbide

  - Plastic: 800 SFM HSS, 1800 SFM carbide

When the feed speed calculator output needs tuning

If the chip is dust and the cut sounds like a scream, feed is too light. If the tool is chattering or flexing, RPM is too high or depth of cut is too deep. The calculator gives a starting point, not a final answer. Bump feed in 10 percent steps until the chip color turns light blue in steel (good heat carrying away in the chip) or the chip stays silvery in aluminum (low heat). Drill speed and feed calculator behavior is the same: start conservative, walk it up.

## Frequently Asked Questions

**Q: How does a feed speed calculator work?**

A: It runs two equations. First, RPM = (SFM x 12) / (pi x D) converts the desired surface cutting speed into spindle RPM. Second, feed rate = RPM x chip load x flutes converts RPM into inches per minute. The calculator looks up SFM and chip load from a material table so you only enter diameter, material, and flutes.

**Q: What feed and speed should I use for a 1/4 inch end mill in aluminum?**

A: For a 2-flute 1/4 inch carbide end mill in 6061 aluminum at 1200 SFM, the calculator returns about 18,335 RPM and 110 IPM. Most hobby CNCs top out at 8,000-12,000 RPM; if that is you, cap RPM at machine max and feed = capped_RPM x chip_load x flutes.

**Q: How is this different from a drill speed and feed calculator?**

A: Milling feed is chip-load-per-tooth times flutes times RPM. Drilling feed is feed-per-revolution times RPM, no flute multiplier because a drill is effectively one cutting edge per revolution. This calculator handles milling. For drilling specifically, use the drill feed and speed calculator.

**Q: Why does flute count affect feed rate?**

A: Each flute removes one chip per revolution. Double the flutes and you can double the feed rate without changing the chip thickness each tooth removes. That is why 4-flute end mills feed faster than 2-flute in the same material, as long as the flutes have room to clear chips.

**Q: Should I use HSS or carbide?**

A: Carbide for anything in production and anything harder than aluminum. HSS for one-off jobs, ductile materials, and when interrupted cuts shock-load the tool. Carbide is 2-3x faster but chips on shock. HSS is tougher but wears fast at high temperature.

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Source: https://vastcalc.com/calculators/physics/feed-speed
Category: Physics
Last updated: 2026-04-08