# Feed and Speed Calculator for Milling

Feed and speed calculator for milling. Get spindle RPM, feed rate (IPM or mm/min), chip load per tooth, SFM, and MRR from end mill diameter, flute count, material, and depth/width of cut.

## What this calculates

A feed and speed calculator milling setup resolves to two numbers the machine control actually reads: spindle RPM and feed rate. This calculator takes end mill geometry (diameter, flutes), workpiece material, and the depth and width of cut, then returns RPM, IPM, chip load per tooth, SFM, metric feed rate, and material removal rate. A chip-thinning factor is applied automatically when the radial engagement is less than half the tool diameter, the single biggest source of feed-rate error in a quick hand calculation.

## Inputs

- **End Mill Diameter** (in) — min 0.001 — Cutting diameter of the end mill or face mill.
- **Number of Flutes** — min 1, max 12 — 2-3 for aluminum, 4 for steel roughing, 5-7 for stainless finishing.
- **Workpiece Material** — options: Aluminum 6061, Mild steel / 1018, Alloy steel / 4140, Stainless 304, Stainless 316, Tool steel (A2, D2), Cast iron, Brass, Titanium Ti-6Al-4V, Inconel 718, Plastic (Delrin, UHMW)
- **Tool Material** — options: HSS, Solid carbide / carbide insert — Carbide runs 2.5-4x the SFM of HSS.
- **Axial Depth of Cut (Ap)** (in) — min 0 — Depth the end mill plunges into the work on each pass.
- **Radial Width of Cut (Ae)** (in) — min 0 — Full slot = tool diameter. Less than D/2 triggers chip thinning.

## Outputs

- **Spindle Speed** (RPM) — Spindle RPM = (SFM x 12) / (pi x D).
- **Cutting Speed** (SFM) — Surface feet per minute for chosen material and tool.
- **Chip Load per Tooth** (IPT) — IPT adjusted for chip thinning when radial engagement is under 50 percent.
- **Feed Rate** (IPM) — Feed rate (IPM) = RPM x chip load x flutes.
- **Feed Rate** (mm/min) — Feed rate in millimeters per minute.
- **Material Removal Rate** (in^3/min) — MRR = axial depth x radial width x feed rate.

## Details

The two milling equations

A feed and speed calculator milling result is always these two equations:

  - RPM = (SFM x 12) / (pi x D) where D is end mill diameter in inches.

  - Feed rate (IPM) = RPM x chip load x flutes.

For a 1/2 inch 3-flute carbide end mill in 6061 aluminum at 1400 SFM and 0.004 IPT: RPM = (1400 x 12) / (pi x 0.5) = 10,695 RPM. Feed rate = 10,695 x 0.004 x 3 = 128.3 IPM. At 0.1 inch axial depth and full slot, MRR = 0.1 x 0.5 x 128.3 = 6.4 in^3/min.

SFM reference for milling

  
    MaterialHSS SFMCarbide SFMCarbide chip load (0.5 in D)
  
  
    Aluminum 606160014000.004 IPT
    Mild steel (1018)1004000.002 IPT
    Alloy steel (4140)702800.0015 IPT
    Stainless 304602200.0015 IPT
    Titanium Ti-6Al-4V401200.001 IPT
    Inconel 71820800.0008 IPT
    Plastic (Delrin)80020000.005 IPT
  

Chip thinning and radial engagement

When radial width of cut (Ae) drops below half the tool diameter, each flute sees a thinner chip than the programmed IPT because it only contacts the work across a shallow arc. The Sandvik correction scales chip load up by D / (2 x sqrt(Ae x (D - Ae))). At Ae = 10 percent of diameter the factor is about 1.67x. This calculator applies the correction so the programmed feed rate produces the target chip thickness at the tooth.

Imperial, metric, and mm/min

A feed and speed calculator milling setup has to work in both unit systems. The RPM equation is unit-independent when metric diameters use RPM = (Vc x 1000) / (pi x D_mm) with Vc in m/min. Feed rate in mm/min = IPM x 25.4. Every output in this calculator is returned in both imperial and metric so controls programmed in either system can use the result directly.

## Frequently Asked Questions

**Q: How do I calculate feed and speed for milling?**

A: Use RPM = (SFM x 12) / (pi x D) and feed rate (IPM) = RPM x chip load x flutes. For a 3/8 inch 2-flute carbide end mill in aluminum at 1400 SFM and 0.003 IPT: RPM = (1400 x 12) / (pi x 0.375) = 14,260 RPM, feed = 14,260 x 0.003 x 2 = 85.6 IPM. This feed and speed calculator milling handles both steps with automatic chip-thinning correction.

**Q: What chip load should I use for an end mill in steel?**

A: For a 1/2 inch end mill in 1018 mild steel, 0.002 IPT is a safe baseline. Alloy steel (4140) drops to 0.0015 IPT. Stainless is 0.0015 IPT. Hardened tool steel is 0.001 IPT. Smaller diameters use less (0.001 at 1/8 inch), larger diameters use more (0.0025 at 3/4 inch). Start at these values; dial feed up 10-20 percent if the chips come off silver and straight.

**Q: How does chip thinning affect feed rate?**

A: When radial engagement is less than half the tool diameter, the chip each flute sees is thinner than the programmed IPT. To keep chip load on the tooth at its target, feed rate must increase. The Sandvik factor D / (2 x sqrt(Ae x (D - Ae))) gives the multiplier. At Ae = 10 percent of D, feed goes up 67 percent. The calculator applies this automatically.

**Q: Does this work for metric milling?**

A: Yes. Diameter and depth accept millimeters via the unit toggle, and the calculator returns feed rate in both IPM and mm/min. Metric cutting speed (Vc in m/min) relates to SFM by Vc = SFM x 0.3048, and the metric RPM equation is RPM = (Vc x 1000) / (pi x D_mm). Same physics, different unit labels.

**Q: Can I use this for a Haas, Tormach, or Mazak mill?**

A: Yes. The cutting speed equation is the same on every CNC controller. A Haas VF, Tormach PCNC, Mazak VTC, and Okuma Genos all accept the RPM and IPM this calculator returns. Machine posts differ but the spindle and feed commands are the same. Start at 80 percent of calculated feed for first-cut safety, then dial up based on chip behavior.

**Q: What is material removal rate (MRR) and why does it matter?**

A: MRR = axial depth x radial width x feed rate, measured in cubic inches per minute. A 1/2 inch end mill in aluminum at 0.1 inch deep, 0.5 inch wide, 128 IPM gives 6.4 in^3/min. MRR is the production shop metric for how fast a part gets made. Higher MRR means shorter cycle time, but it trades off against tool life and surface finish.

---

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