# CNC Feed Rate Calculator

CNC feed rate calculator. Enter spindle RPM, chip load per tooth, and flute count to get feed rate in IPM and mm/min. Works for metals, hardwood, MDF, plastic, and foam.

## What this calculates

A CNC feed rate calculator turns spindle RPM, chip load per tooth, and flute count into the feed rate a CNC control needs. Output is given in both IPM (imperial, most Haas and Fadal controls) and mm/min (metric, most DMG Mori and Mazak controls), so the same numbers work on any machine. Chip load defaults scale with tool diameter and match the values in Harvey Tool, Helical, and Sandvik data books.

## Inputs

- **RPM Source** — options: Enter RPM directly, Compute from diameter + SFM — Compute mode uses (SFM x 12) / (pi x D).
- **Cutter Diameter** (in) — min 0.001 — Tool diameter. Used in compute mode for the SFM-to-RPM conversion.
- **Spindle RPM** (RPM) — min 1 — Used when RPM Source = Enter directly.
- **Material** — options: Aluminum, Mild steel / 1018, Alloy steel / 4140, Stainless steel, Cast iron, Brass, Titanium, Hardwood, Softwood, MDF, Plywood, Plastic — Used for the default chip load and (in compute mode) for SFM lookup.
- **Cutter Material** — options: HSS, Carbide — Used only in compute mode for the SFM lookup.
- **Flutes** — min 1, max 8 — Number of cutting edges.
- **Chip Load Override** (in/tooth) — min 0 — Override the material chip load with a vendor-specified value.

## Outputs

- **Feed Rate (IPM)** (in/min) — Feed rate in inches per minute.
- **Feed Rate (metric)** (mm/min) — Feed rate in mm/min for metric CNC controls.
- **Chip Load Used** (IPT) — Chip load per tooth applied.
- **Spindle RPM Used** (RPM) — Direct entry or computed from SFM.
- **Cutting Speed** (SFM) — SFM reference for the material + tool.

## Details

CNC feed rate formula

The CNC feed rate equation is the same whether you program a VMC, a CNC router, or a high-speed lathe:

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

  - Metric: Feed rate (mm/min) = IPM x 25.4.

  - For compute mode: RPM = (SFM x 12) / (pi x D).

Example: 1/4 inch 2-flute carbide end mill in 6061 aluminum. SFM target = 1500. RPM = (1500 x 12) / (pi x 0.25) = 22,918 RPM. Chip load = 0.003 IPT (0.004 baseline scaled 0.75 for 1/4 inch tool). Feed rate = 22,918 x 0.003 x 2 = 137.5 IPM = 3,492 mm/min. If the CNC maxes at 12,000 RPM, cap there and recompute feed: 12,000 x 0.003 x 2 = 72 IPM.

CNC feed rate calculator metric support

A CNC feed rate calculator metric workflow is identical to imperial once tool diameter is set in mm. RPM calculation is unit-independent. Feed rate in mm/min equals IPM x 25.4. For European CNCs running Siemens 840D or Heidenhain TNC7, the mm/min output goes straight into the F word of your G-code. A Haas, Fanuc, or Mazak control accepts either IPM (G94/G95 inch mode) or mm/min (G21 metric mode). This calculator returns both.

Chip load per tooth by material

  
    MaterialChip load (IPT)
  
  
    Aluminum 60610.004
    Mild steel (1018)0.002
    Alloy steel (4140)0.0015
    Stainless steel0.0015
    Titanium Ti-6Al-4V0.001
    Brass0.003
    Hardwood0.008
    Softwood0.012
    MDF0.010
    Plywood0.009
    Plastic (Delrin, acrylic)0.005
  

Small-tool chip load scaling

A 1/16 inch end mill cannot take the full chip load a 1 inch end mill can. The flute is smaller, the cutter is less rigid, and cutting force matters more per unit of tool stiffness. This CNC feed rate calculator scales chip load to 50 percent under 1/8 inch, 75 percent for 1/8-1/4 inch, and 125 percent over 3/4 inch. Override the auto-scaling with the chip load override field if you have vendor-specific data.

Feed rate vs spindle RPM

Spindle RPM comes from the cutting speed (SFM), which depends on material and tool material. Feed rate comes from RPM times chip load times flutes. Changing chip load does not change RPM; changing SFM does not change chip load. They are independent inputs the CNC program sees as two separate words (S for spindle, F for feed). A CNC feed rate calculator helps you set F without touching S.

## Frequently Asked Questions

**Q: How do I calculate CNC feed rate?**

A: Feed rate (IPM) = RPM x chip load per tooth x number of flutes. For a 1/4 inch 2-flute carbide end mill in aluminum at 22,918 RPM and 0.003 IPT chip load, feed = 22,918 x 0.003 x 2 = 137.5 IPM. This CNC feed rate calculator does the conversion in one step.

**Q: Does this CNC feed rate calculator support metric?**

A: Yes. Tool diameter accepts millimeters via the unit toggle. Feed rate is returned in both IPM (imperial) and mm/min (metric), so a CNC feed rate calculator metric workflow is a single unit setting away. The IPM-to-mm/min conversion is IPM x 25.4.

**Q: What chip load should I use for aluminum?**

A: 0.003-0.005 IPT for most end mills in 6061 aluminum. Small tools (1/8 and under) scale down to about 0.002 IPT; tools over 3/4 inch can push 0.005+ IPT. This CNC feed rate calculator uses 0.004 IPT as the aluminum baseline with diameter-based scaling.

**Q: Why does flute count affect feed rate?**

A: Each flute removes one chip per revolution. Doubling flutes doubles feed rate at the same chip load per tooth. That is why a 4-flute end mill feeds 2x faster than a 2-flute in the same material (as long as chip evacuation is adequate). Aluminum is usually 2-flute for chip room; steel is 3-4 flute.

**Q: What is the difference between feed rate and spindle speed?**

A: Spindle speed (S word in G-code, RPM) is how fast the tool rotates. Feed rate (F word, IPM or mm/min) is how fast the tool advances through the material. They are independent: change S without changing F, or vice versa. Both set chip thickness per tooth via feed = RPM x chip load x flutes.

**Q: When do I use IPM vs mm/min?**

A: IPM on an imperial CNC (G20 mode, Haas, Fadal). mm/min on a metric CNC (G21 mode, DMG Mori, Mazak, Siemens). Both are the same velocity, just different units: mm/min = IPM x 25.4. This calculator returns both, so you can paste the right one into your F word.

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