# Mill Feed Rate Calculator

Mill feed rate calculator. Compute feed rate (IPM), feed per tooth (IPT), and feed per revolution from spindle RPM, flute count, chip load, and material. Includes chip-thinning correction for shallow radial cuts.

## What this calculates

Feed rate on a milling machine is the linear speed at which the cutter advances into the work, usually expressed in inches per minute (IPM) or millimeters per minute (mm/min). It depends on spindle RPM, flute count, and the chip load each tooth is supposed to take. This mill feed rate calculator takes those inputs, applies a chip-thinning correction when radial width is less than half the tool diameter, and returns IPM, IPT, IPR, and metric feed rate in one step.

## Inputs

- **Spindle Speed** (RPM) — min 0 — Spindle RPM. Use a cutting speed calculator first if you need to derive this from SFM.
- **Number of Flutes** — min 1, max 16 — 2-3 for aluminum, 4 for steel, 5-7 for stainless finishing.
- **Workpiece Material** — options: Aluminum (0.004 IPT base), Mild steel (0.002 IPT base), Alloy steel 4140 (0.0015 IPT), Stainless (0.0015 IPT), Tool steel (0.001 IPT), Cast iron (0.003 IPT), Brass (0.003 IPT), Titanium (0.001 IPT), Inconel 718 (0.0008 IPT), Plastic Delrin (0.005 IPT) — Used to pull the default IPT baseline. Override below if your tool vendor publishes a value.
- **Chip Load Override (IPT)** (in/tooth) — min 0 — Optional. Enter a specific chip load if your tool catalog lists one.
- **Tool Diameter (optional)** (in) — min 0 — Used only for chip-thinning correction. Leave 0 to skip.
- **Radial Width of Cut (optional)** (in) — min 0 — Optional. When Ae < D/2, chip thinning is applied to raise feed rate.

## Outputs

- **Feed Rate** (IPM) — Feed rate in inches per minute = RPM x IPT x flutes.
- **Feed Rate** (mm/min) — Feed rate in millimeters per minute.
- **Feed per Tooth** (IPT) — Effective chip load per tooth after chip thinning.
- **Feed per Revolution** (in/rev) — IPR = IPT x flutes.
- **Chip Thinning Factor** — Multiplier applied when radial width is less than D/2.

## Details

The mill feed rate formula

Feed rate on an end mill is:

Feed rate (IPM) = RPM x chip load per tooth x number of flutes

Example: a 4-flute end mill spinning 3,056 RPM in mild steel with a 0.002 inch chip load runs at 3,056 x 0.002 x 4 = 24.4 IPM. That result is the feed value programmed into a G-code F word.

Chip load per tooth by material

  
    MaterialBaseline IPT (0.5 in D)
  
  
    Aluminum0.004
    Mild steel (1018)0.002
    Alloy steel (4140)0.0015
    Stainless 3040.0015
    Tool steel0.001
    Cast iron0.003
    Brass0.003
    Titanium Ti-6Al-4V0.001
    Inconel 7180.0008
    Plastic (Delrin)0.005
  

These are a 1/2 inch end mill baseline. Scale down 25-50 percent for tools 1/8 inch and smaller; scale up 25 percent for tools 3/4 inch and larger.

Chip thinning and radial engagement

When the radial width of cut (Ae) is less than half the tool diameter, the chip each tooth sees is thinner than the programmed IPT because the tooth only contacts the work across a shallow arc. The Sandvik chip-thinning correction scales IPT up by D / (2 x sqrt(Ae x (D - Ae))). At Ae = 0.05 inch on a 0.5 inch end mill (10 percent radial) the factor is 1.67x, meaning feed rate can be 67 percent higher than the naive calculation and still keep chip thickness at the cutter target.

Imperial and metric feed rate

This calculator returns feed rate in both IPM and mm/min. A quick conversion: mm/min = IPM x 25.4. Controls from Haas, Fanuc, Heidenhain, and Siemens all accept either unit depending on how the post is configured. When in doubt, program in the same units the drawing calls out; imperial drawings use IPM, metric drawings use mm/min.

## Frequently Asked Questions

**Q: How do I calculate the feed rate for a milling machine?**

A: Feed rate (IPM) = RPM x chip load per tooth x number of flutes. For a 3-flute carbide end mill in aluminum at 10,000 RPM and 0.004 IPT: 10,000 x 0.004 x 3 = 120 IPM. Use this mill feed rate calculator with automatic chip-thinning correction to get the answer in one step.

**Q: What chip load should I use for mild steel?**

A: A 1/2 inch end mill in 1018 mild steel runs 0.002 IPT as a baseline. 4140 alloy steel and 304 stainless drop to 0.0015 IPT. Tool steel and inconel go to 0.001 IPT or lower. Smaller end mills use less (0.001 at 1/8 inch); larger ones use more (0.0025 at 3/4 inch). The calculator pulls a sensible default from the material you pick.

**Q: What is chip thinning and when does it matter?**

A: When the radial width of cut is less than half the tool diameter, the effective chip thickness at the tooth is less than the programmed IPT. If you don't compensate, the tool rubs and generates heat without cutting. The Sandvik correction D / (2 x sqrt(Ae x (D - Ae))) scales chip load up. This calculator applies it automatically when you enter a radial width.

**Q: How do I convert IPM to mm/min?**

A: Multiply IPM by 25.4. So 24.4 IPM is 620 mm/min, 120 IPM is 3,048 mm/min. Controls from Haas, Tormach, Mazak, Okuma, Doosan, and Fanuc all accept either unit depending on post configuration. This calculator returns both values, so you can paste either one straight into your G-code.

**Q: Can I use this calculator for high-feed milling?**

A: Yes, but use the chip load override. High-feed mills (like Ingersoll Hi-Feed or Iscar Heli2000) are geometry-specific and published chip loads are often 0.010-0.025 IPT, far above the baseline in this calculator. Pull IPT from the manufacturer catalog and override. The RPM and flute multiplication work the same.

**Q: What is feed per revolution (IPR) and when do I use it?**

A: IPR is feed per one spindle revolution, equal to IPT x flutes. Lathes program feed in IPR because chip thickness is set per revolution. Mills program in IPM but some controllers also accept IPR. The calculator returns both so you can use whichever one your post expects.

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