# End Mill Speeds and Feeds Calculator

End mill speeds and feeds calculator. Enter diameter, flutes, and material to get RPM, feed rate (IPM / mm/min), chip load, SFM / Vc, and MRR. Imperial and metric, with chip-thinning correction.

## What this calculates

An end mill speeds and feeds calculator resolves end mill geometry plus workpiece material into two numbers every CNC control reads: spindle RPM and feed rate. This calculator adds chip load, SFM, metric cutting speed, and material removal rate, with a chip-thinning correction applied when radial engagement is less than half the tool diameter. Works equally well as an end mill speeds and feeds calculator metric setup for shops that program in mm/min.

## Inputs

- **End Mill Diameter** (in) — min 0.001 — Cutting diameter of the end mill.
- **Flutes** — min 1, max 12 — Number of cutting edges.
- **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)
- **End Mill Material** — options: HSS (high-speed steel), Solid carbide — Carbide runs 2.5-4x the SFM of HSS.
- **Axial Depth (Ap)** (in) — min 0 — Depth of cut per pass.
- **Radial Depth (Ae)** (in) — min 0 — Radial engagement. Full slot = D. 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 the material / tool pair.
- **Cutting Speed** (m/min) — Metric cutting speed (Vc).
- **Chip Load** (IPT) — Feed per tooth after chip thinning.
- **Feed Rate** (IPM) — Linear feed in inches per minute.
- **Feed Rate** (mm/min) — Linear feed in millimeters per minute.
- **Material Removal Rate** (in^3/min) — MRR = axial x radial x feed rate.

## Details

The end mill formulas

  - RPM = (SFM x 12) / (pi x D) in imperial, or RPM = (Vc x 1000) / (pi x D_mm) in metric.

  - Feed rate (IPM) = RPM x chip load x flutes, or feed rate (mm/min) = IPM x 25.4.

  - MRR = axial depth x radial depth x feed rate.

For a 3/8 inch 3-flute carbide end mill in 4140 alloy steel (280 SFM, 0.0015 IPT): RPM = (280 x 12) / (pi x 0.375) = 2,852. Feed rate = 2,852 x 0.0015 x 3 = 12.8 IPM. At 0.1 inch axial and 0.188 inch radial (half slot), MRR = 0.1 x 0.188 x 12.8 = 0.24 in^3/min.

SFM reference

  
    WorkpieceHSS SFMCarbide SFMVc (m/min, carbide)
  
  
    Aluminum 60616001400427
    Mild steel 1018100400122
    Alloy steel 41407028085
    Stainless 3046022067
    Stainless 3165020061
    Titanium Ti-6Al-4V4012037
    Inconel 718208024
    Plastic (Delrin)8002000610
  

Chip thinning and HSM toolpaths

When radial engagement drops below half the tool diameter, the actual chip thickness is thinner than the programmed IPT and feed must rise to restore target chip thickness. The Sandvik chip-thinning factor D / (2 x sqrt(Ae x (D - Ae))) is the industry-standard correction. At Ae = 0.05 inch on a 0.5 inch end mill (10 percent radial) the factor is 1.67x. HSM and trochoidal milling strategies rely on this correction to run 2-3x faster than conventional slot milling without burning the tool.

End mill speeds and feeds calculator metric

For an end mill speeds and feeds calculator metric workflow, this calculator returns feed rate and cutting speed in mm/min and m/min alongside the imperial values. Enter diameter and depths in mm via the unit toggle; all outputs return in both systems. Metric users in the EU, UK, Japan, and Australia can paste mm/min feeds straight into their G-code. The chip-thinning correction is unit-independent.

## Frequently Asked Questions

**Q: How do I calculate speeds and feeds for an end mill?**

A: RPM = (SFM x 12) / (pi x D), and feed rate (IPM) = RPM x chip load x flutes. For a 1/2 inch 3-flute carbide end mill in aluminum at 1400 SFM and 0.004 IPT: RPM = 10,695, feed = 10,695 x 0.004 x 3 = 128.3 IPM. This end mill speeds and feeds calculator does both steps with automatic chip-thinning correction.

**Q: Does this calculator work in metric?**

A: Yes. The end mill speeds and feeds calculator metric output gives feed rate in mm/min and cutting speed in m/min (Vc). Diameter and depth inputs accept mm via the unit toggle. The metric RPM formula RPM = (Vc x 1000) / (pi x D_mm) is equivalent to the imperial one; the calculator returns both systems simultaneously.

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

A: A 1/2 inch carbide end mill in mild steel runs 0.002 IPT as a baseline. Alloy steels like 4140 drop to 0.0015 IPT. Tool steel or hardened steel goes to 0.001 IPT. Smaller end mills use less (0.001 at 1/8 inch). This calculator scales the base chip load by diameter automatically.

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

A: When the radial engagement of the cut is less than half the tool diameter, each flute only contacts the work across a shallow arc, so the chip it removes is thinner than the programmed IPT. Chip thinning compensates by raising feed rate. The correction factor is D / (2 x sqrt(Ae x (D - Ae))). Without it, shallow radial cuts rub and burn the tool.

**Q: Can I use this for HSM and trochoidal toolpaths?**

A: Yes, and you should. Trochoidal milling strategies (Adaptive, Dynamic OptiRough) use shallow radial engagement with deep axial engagement, which maxes out the chip-thinning correction. Feed rates run 2-3x the conventional milling number. Enter small radial depth (5-15 percent of diameter) and the calculator raises feed rate automatically via the thinning factor.

**Q: How do I know if my numbers are right?**

A: Listen and look. A balanced end mill cut sings steady; chatter rattles. Chips come off shiny and curled in aluminum, light straw in steel. If chips come off blue, you are cooking the tool, slow feed or RPM. If chips come off as dust and the tool squeals, chip load is too low or you skipped chip thinning. Start at 80 percent of calculated feed for first cuts.

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Source: https://vastcalc.com/calculators/physics/end-mill-speeds-and-feeds
Category: Physics
Last updated: 2026-04-08