# Cutting Speed Calculator for Milling

Cutting speed calculator for milling. Enter end mill diameter, workpiece material, and tool material to get spindle RPM and SFM. Works for HSS, carbide, aluminum, steel, stainless, and titanium.

## What this calculates

The cutting speed of a milling operation is the surface speed at which the outside edge of the end mill passes through the workpiece. It is measured in SFM (surface feet per minute) or m/min, and it is the single number that connects a material to a spindle RPM. Pick the wrong SFM and your end mill wears out in minutes or rubs without cutting at all. This calculator looks up the right SFM for your material and tool, then converts it to spindle RPM.

## Inputs

- **Cutter Diameter** (in) — min 0.001 — End mill or face mill diameter.
- **Workpiece Material** — options: Aluminum 6061 (600/1400 SFM), Mild steel / 1018 (100/400 SFM), Alloy steel / 4140 (70/280 SFM), Stainless 304 (60/220 SFM), Stainless 316 (50/200 SFM), Tool steel (50/180 SFM), Cast iron (80/260 SFM), Brass (250/500 SFM), Bronze (150/350 SFM), Titanium Ti-6Al-4V (40/120 SFM), Inconel 718 (20/80 SFM), Plastic / Delrin (800/2000 SFM) — Workpiece material. Values are HSS / carbide SFM baselines.
- **Tool Material** — options: HSS (high-speed steel), Solid carbide or insert — Carbide runs roughly 3x the SFM of HSS in most metals.
- **SFM Override** (SFM) — min 0 — Optional. Override the default SFM with a manufacturer-specific value from a tool catalog.

## Outputs

- **Spindle Speed** (RPM) — Spindle RPM from the cutting speed equation.
- **Cutting Speed** (SFM) — Surface feet per minute used to drive the RPM calculation.
- **Cutting Speed** (m/min) — Surface speed in meters per minute (metric).
- **Rim Speed** (ft/min) — Linear speed at the cutter circumference at the calculated RPM.

## Details

The cutting speed equation

The cutting speed calculator milling formula is unchanged since the Machinery's Handbook first published it:

RPM = (SFM x 12) / (pi x D)

SFM is the surface speed for your material and tool. D is the end mill diameter in inches. The 12 converts feet to inches so the units cancel cleanly. For a 1/2 inch carbide end mill in 6061 aluminum at 1400 SFM: RPM = (1400 x 12) / (pi x 0.5) = 10,695 RPM.

SFM values by material and tool

  
    MaterialHSS SFMCarbide SFM
  
  
    Aluminum 60616001400
    Mild steel (1018)100400
    Alloy steel (4140)70280
    Stainless 30460220
    Stainless 31650200
    Cast iron80260
    Titanium Ti-6Al-4V40120
    Inconel 7182080
    Plastic (Delrin)8002000
  

Carbide consistently runs 2.5x to 4x the SFM of HSS because carbide stays hard past 1800 F while HSS softens at 1000 F. Every cutting speed calculator for milling should show both columns so you can see the difference.

Metric milling speed (Vc)

Outside North America, milling cutting speed is measured in meters per minute (m/min or Vc). The conversion is Vc (m/min) = SFM x 0.3048. The RPM equation in metric form is RPM = (Vc x 1000) / (pi x D) with diameter in millimeters. A 12 mm carbide end mill in mild steel at 120 m/min gives RPM = (120 x 1000) / (pi x 12) = 3,183 RPM. This calculator returns both SFM and m/min so you can work in whichever system your control uses.

When to adjust the default SFM

The defaults are safe midpoints. Use the SFM override when a tool manufacturer publishes a speed for their specific geometry (Harvey Tool, Destiny Tool, YG-1, Seco). High-feed mills and trochoidal toolpaths can push SFM 30-50 percent above the table. Old machines with loose spindles, long stickout end mills, or heavy radial engagement should run 20-30 percent below the table. Chip color tells you whether you are in the zone: light straw in steel, silver in aluminum.

## Frequently Asked Questions

**Q: How do I calculate cutting speed for milling?**

A: Use RPM = (SFM x 12) / (pi x D), where SFM is the surface speed for your material and tool material and D is the end mill diameter in inches. For a 1/2 inch carbide end mill in mild steel at 400 SFM: RPM = (400 x 12) / (pi x 0.5) = 3,056 RPM. This calculator pulls SFM from a material table automatically.

**Q: What is SFM in milling?**

A: SFM is surface feet per minute, the linear speed of the cutting edge at the outer diameter of the end mill. It is the property of the material and tool combination. Aluminum with carbide is about 1400 SFM; mild steel with HSS is about 100 SFM. SFM drives RPM through the cutting speed equation but is itself independent of the tool size.

**Q: Why does carbide run so much faster than HSS?**

A: Carbide maintains hardness up to about 1800 F; HSS softens near 1000 F. In milling, the cutting edge temperature spikes fast, so tool material that can shrug off heat cuts faster. In aluminum, carbide runs 2.5x the HSS SFM. In steel, 4x. That is why every CNC production shop uses carbide end mills even for simple parts.

**Q: How do I convert SFM to m/min for metric milling?**

A: Multiply SFM by 0.3048. 100 SFM is 30.5 m/min, 400 SFM is 122 m/min, 1400 SFM is 427 m/min. The RPM equation in metric is RPM = (Vc x 1000) / (pi x D) with D in millimeters. This cutting speed calculator milling returns both SFM and m/min in the output list.

**Q: What cutting speed should I use for stainless steel?**

A: Stainless 304 runs 60 SFM with HSS end mills and 220 SFM with carbide. Stainless 316 is slightly slower at 50 / 200 SFM. Stainless work-hardens under a slow, rubbing cut, so it is critical to keep chip load up and not pause the cutter mid-pass. Use a sharp end mill and high-pressure coolant if you have it.

**Q: Does the spindle RPM need to match the calculated value exactly?**

A: No. Machine the value to the nearest available spindle step, then listen. A well-balanced cut sings steady; chatter sounds like a rattle. Round to the nearest 50 RPM for belt-drive spindles. Direct-drive CNC spindles can hit the calculated value within 1 RPM, so the calculator output is the programmed value.

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