# End Mill Cutting Speed Calculator

End mill cutting speed calculator. Enter end mill diameter, material, and tool material to get spindle RPM, SFM, and m/min. Covers HSS, carbide, and every common shop material, imperial and metric.

## What this calculates

The cutting speed of an end mill is the linear speed of its outer cutting edge as it passes through the workpiece. Measured in SFM (surface feet per minute) in North America or Vc (m/min) elsewhere, it is the property that ties the workpiece material and tool to a spindle RPM. Pick the wrong SFM and the end mill burns up or rubs. This calculator looks up the SFM for your material-tool pair and converts it to spindle RPM.

## Inputs

- **End Mill Diameter** (in) — min 0.001 — Cutting diameter of the end mill.
- **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 A2/D2 (50/180 SFM), Cast iron (80/260 SFM), Brass (250/500 SFM), Titanium Ti-6Al-4V (40/120), Inconel 718 (20/80 SFM), Plastic Delrin (800/2000 SFM)
- **End Mill Material** — options: HSS (high-speed steel), Solid carbide — Carbide runs 2.5-4x the SFM of HSS.
- **SFM Override** (SFM) — min 0 — Optional. Use a tool vendor's published SFM for their specific geometry.

## Outputs

- **Spindle Speed** (RPM) — Spindle RPM = (SFM x 12) / (pi x D).
- **Cutting Speed** (SFM) — Surface feet per minute.
- **Cutting Speed** (m/min) — Metric cutting speed Vc.
- **Spindle Speed (metric diameter)** (RPM) — RPM cross-check using the metric form RPM = (Vc x 1000) / (pi x D_mm).

## Details

The end mill cutting speed equation

The end mill cutting speed calculator formula comes straight from Machinery's Handbook:

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

SFM is surface feet per minute for the material and tool pair. D is end mill diameter in inches. The 12 converts feet to inches so units cancel. Metric form: RPM = (Vc x 1000) / (pi x D_mm) with Vc in m/min and D in millimeters.

Example: a 1/2 inch carbide end mill in 4140 alloy steel at 280 SFM has RPM = (280 x 12) / (pi x 0.5) = 2,139 RPM. Converted to metric: D = 12.7 mm, Vc = 85 m/min, RPM = (85 x 1000) / (pi x 12.7) = 2,130 RPM (matches within rounding).

SFM for end mill cutting speed

  
    WorkpieceHSS end mill (SFM)Carbide end mill (SFM)
  
  
    Aluminum 60616001400
    Mild steel 1018100400
    Alloy steel 414070280
    Stainless 30460220
    Stainless 31650200
    Tool steel (A2, D2)50180
    Cast iron80260
    Titanium Ti-6Al-4V40120
    Inconel 7182080
    Plastic (Delrin)8002000
  

HSS vs carbide end mills

HSS holds hardness to about 1000 F. Carbide holds hardness past 1800 F. That higher temperature capacity means carbide can run 2.5-4x the SFM of HSS in the same material. In aluminum, HSS tops out near 600 SFM; carbide cruises at 1400 SFM. In stainless, HSS makes 60 SFM; carbide hits 220 SFM. The calculator picks the right column automatically based on the tool material.

When to override the SFM

Tool manufacturers publish SFM recommendations for their specific geometries. Harvey Tool, Destiny, YG-1, Seco, and Iscar all have online catalogs listing speeds for aluminum, steel, stainless, and exotic alloys. Use the SFM override when the vendor publishes a number for your cutter. Trochoidal and high-feed toolpaths also run SFM 30-50 percent above the generic table because radial engagement is low and the cutting edge sees less heat per revolution.

## Frequently Asked Questions

**Q: How do I calculate the cutting speed of an end mill?**

A: Use RPM = (SFM x 12) / (pi x D), where SFM is the surface feet per minute for your material and tool material and D is the end mill diameter in inches. For a 1/4 inch carbide end mill in aluminum at 1400 SFM: RPM = (1400 x 12) / (pi x 0.25) = 21,390 RPM. This end mill cutting speed calculator handles the lookup and math automatically.

**Q: What is SFM for a carbide end mill in mild steel?**

A: 1018 mild steel runs 400 SFM with a solid carbide end mill. HSS drops to 100 SFM. For a 3/8 inch carbide end mill in 1018: RPM = (400 x 12) / (pi x 0.375) = 4,074 RPM. Scale down 20 percent for long-flute or long-reach tools where the stickout is more than 4x diameter.

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

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 metric RPM formula is RPM = (Vc x 1000) / (pi x D_mm) with Vc in m/min and D in millimeters. The calculator returns both imperial and metric speed values so you can use either system.

**Q: Why does a larger end mill need lower RPM at the same SFM?**

A: Because cutting speed is linear speed at the outside diameter. For a given SFM, a larger tool travels more distance per revolution, so fewer revolutions are needed to cover the same linear distance. RPM = (SFM x 12) / (pi x D) has D in the denominator, so doubling diameter halves RPM. A 1 inch carbide end mill in aluminum at 1400 SFM is only 5,348 RPM.

**Q: Do the cutting speed values vary by end mill vendor?**

A: Yes, by 20-40 percent. Generic catalogs like Machinery's Handbook publish safe midpoints. Premium vendors (Destiny, Harvey Tool, YG-1 Dream Drill) often list 1.3-1.8x those values for their coated carbide geometries. Use the SFM override to feed a vendor-specific number in. Always start at the generic value, then push up if chip color, sound, and tool wear look good.

**Q: Is the cutting speed the same as feed rate?**

A: No. Cutting speed (SFM or m/min) is the linear speed of the cutting edge. Feed rate (IPM or mm/min) is how fast the tool moves through the work. They are related but distinct: cutting speed sets RPM, feed rate depends on RPM and chip load per tooth. This calculator focuses on cutting speed and RPM; a separate feed rate calculator multiplies RPM by chip load and flutes.

---

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