# CNC Speeds and Feeds Calculator

> Source: https://netray.co/tools/cnc-speeds-and-feeds-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Turn a surface speed and chip load into spindle RPM and table feed for any end mill, capped at your machine's maximum RPM.

## Category

manufacturing

## Industry

Machine Shops

## Audience

- CNC machinist
- CNC programmer
- Manufacturing engineer

## Tool

**Kind:** calculator

**Inputs:**

#### Surface speed

**Key:** sfm

**Type:** number

**Default:** 350

**Min:** 1

**Step:** 10

**Unit:** SFM

**Help:** Surface feet per minute from your tool maker's catalog for this material and coating.

#### Cutter diameter

**Key:** dia

**Type:** number

**Default:** 0.5

**Min:** 0.01

**Step:** 0.0625

**Unit:** in

**Help:** Use the actual cutting diameter, not the shank.

#### Number of flutes

**Key:** flutes

**Type:** number

**Default:** 4

**Min:** 1

**Step:** 1

**Unit:** flutes

#### Chip load per tooth

**Key:** fz

**Type:** number

**Default:** 0.003

**Min:** 0.0001

**Step:** 0.0005

**Unit:** in/tooth

**Help:** Feed per tooth from the catalog. Reduce it for slotting or small diameters.

#### Machine maximum spindle speed

**Key:** max_rpm

**Type:** number

**Default:** 12000

**Min:** 100

**Step:** 500

**Unit:** RPM

**Help:** The calculated RPM is capped at this value.

**Outputs:**

#### Ideal RPM (uncapped)

**Key:** calc_rpm

**Expr:** sfm * 12 / (pi * dia)

**Format:** integer

**Description:** RPM = SFM x 12 / (pi x diameter).

#### Programmed spindle speed

**Key:** rpm

**Expr:** min(calc_rpm, max_rpm)

**Format:** integer

**Primary:** true

**Description:** Ideal RPM limited by the spindle maximum.

#### Feed rate

**Key:** feed

**Expr:** rpm * flutes * fz

**Format:** decimal

**Primary:** true

**Description:** Inches per minute = RPM x flutes x chip load.

#### Feed rate (mm/min)

**Key:** feed_mm

**Expr:** feed * 25.4

**Format:** integer

#### Actual surface speed

**Key:** act_sfm

**Expr:** pi * dia * rpm / 12

**Format:** decimal

**Description:** Lower than the target when the spindle limit applies.

#### Actual cutting speed (m/min)

**Key:** vc

**Expr:** act_sfm * 0.3048

**Format:** decimal

**Chart:**

#### Feed rate (IPM) vs surface speed

**Type:** line

**X:** sfm

**From:** 100

**To:** 1000

**Steps:** 30

**Series:**

- feed

**Disclaimer:** Starting values only. Confirm against your tool manufacturer's data and your machine, fixture and workpiece rigidity before cutting.

## Content

**Intro:** Speeds and feeds decide tool life, cycle time and finish. This calculator converts a catalog surface speed and chip load into the RPM and feed rate you type into your program, and tells you when your spindle limit changes the answer.

**Sections:**

#### How to use the calculator

**Body:** Start with the surface speed (SFM) and chip load per tooth that your cutter manufacturer lists for your workpiece material. Enter the cutter diameter and flute count, then your machine's maximum RPM. The calculator returns the ideal RPM, the RPM actually programmed after the spindle cap, the feed in inches per minute and millimeters per minute, and the real surface speed you end up running. The chart shows how feed changes as you raise or lower SFM, which helps when you are tuning a job and want to see the cycle time cost of running cooler.

**Bullets:**

- Use catalog values as the starting point, not the finish line.
- Enter the cutting diameter, not the shank diameter.
- Check the capped RPM against the actual SFM before accepting the feed.

#### The formulas behind it

**Body:** Surface speed is how fast the cutting edge travels past the material: SFM = pi x diameter x RPM / 12 when diameter is in inches. Rearranged, RPM = SFM x 12 / (pi x diameter), which is the familiar shortcut of about 3.82 x SFM / diameter. Feed rate then follows from chip load: IPM = RPM x number of flutes x chip load per tooth. Metric users can use Vc in meters per minute with RPM = 1000 x Vc / (pi x diameter in mm), which is the same relationship in different units.

#### Worked example

**Body:** A half inch four flute carbide end mill in aluminum at 350 SFM gives an ideal RPM of about 2,674. At 0.003 inch per tooth the feed is 2,674 x 4 x 0.003, roughly 32 IPM. On a small high speed machine the same cutter could run at 800 SFM or more and the spindle cap would start to matter: if RPM is limited to 12,000 the actual surface speed is lower than the target and the feed must be recalculated from the capped RPM, which this tool does for you.

#### Common mistakes

**Body:** The most common error is using a chip load that ignores the cut. In slotting the full diameter is engaged and heat has nowhere to go, so lower SFM and feed. In light radial cuts, chip thinning means the true chip is thinner than the programmed feed per tooth, so many shops raise the feed to compensate. Other mistakes include mixing metric and inch values, forgetting that long stickout reduces usable speed, and ignoring the machine's actual power at low RPM.

**Cta:** If your programs live in an ERP or MES, Netray can help surface the routing data, tooling and run-time standards behind them so cutting data is reviewed against real job history.

**Faq:**

#### How do I convert SFM to RPM?

**Answer:** Use RPM = SFM x 12 / (pi x diameter in inches), or roughly 3.82 x SFM divided by the diameter. For metric, RPM = 1000 x Vc in meters per minute / (pi x diameter in millimeters). This calculator does the conversion and applies your spindle limit.

#### What chip load should I use?

**Answer:** Use the value your tool manufacturer lists for the cutter diameter, material and type of cut. Smaller diameters need much smaller chip loads. The companion chip load worksheet on this site gives typical starting ranges for common materials.

#### What if my calculated RPM is higher than my spindle can run?

**Answer:** Cap the RPM at the spindle maximum and recalculate feed from the capped value. You lose some surface speed, so you also lose some productivity, but the cut remains stable. This tool shows both ideal and capped values.

#### Does this work for turning or drilling?

**Answer:** The RPM formula works for any rotating cutter or workpiece diameter. For turning, feed is per revolution rather than per tooth, so multiply RPM by feed per revolution. For drilling use feed per revolution with the drill diameter.

## Search terms

speeds and feeds calculator, cnc speeds and feeds calculator, milling rpm calculator, feed rate calculator milling, sfm to rpm calculator, end mill speeds and feeds, chip load calculator, ipm calculator cnc

---
Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json