Machining calculators · United States · 2026

SFM Calculator for Surface Feet per Minute & RPM

Calculate surface speed from cutter diameter and spindle RPM—or solve for RPM from a target SFM. Then move directly into feeds, drilling, turning and milling calculations.

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No signupRuns in your browserFormula shownUS inch units first
π-based formulaDeterministic outputManufacturer data stays user-controlled

Surface speed calculator

Choose what you want to solve for.

Result—
Input reference—

This calculator performs the geometric conversion only. Use cutting data from your tool manufacturer for the appropriate SFM for the tool, material and operation.

Checked relationship: SFM = π × diameter × RPM ÷ 12. Example: 0.500 in at 5,000 RPM = 654.5 SFM.
8 machining toolsOne focused job per calculator
Instant calculationNo server round-trip
Transparent formulasSee how results are derived
Built for machinistsMilling, drilling & turning

Calculator clusters

Choose the machining operation

Start with the task rather than hunting through one oversized form. Each calculator solves one primary machining problem and links to the next useful calculation.

01 · CORE

Surface speed & spindle

Move between SFM, tool diameter and RPM.

Spindle speed →
03 · HOLEMAKING

Drilling & reaming

Convert cutting speed and feed per revolution into shop-ready RPM and IPM.

Drill calculator →

All tools

Machining calculators

Search the current toolset. The architecture is intentionally compact so each URL has a distinct purpose.

8 calculators
SFM

SFM Calculator

Calculate surface feet per minute or RPM from cutter diameter.

Open calculator → General

Cutting Speeds & Feeds Calculator

Calculate RPM, feed rate, chip load per revolution and MRR.

Open calculator → Drilling

Drill Speed & Feed Calculator

Convert drill diameter, SFM and feed per revolution into RPM and IPM.

Open calculator → Milling

End Mill Speeds & Feeds Calculator

Calculate end mill RPM, IPM, IPR and material removal rate.

Open calculator → Turning

Lathe Speeds & Feeds Calculator

Calculate turning RPM, feed rate and estimated material removal rate.

Open calculator → Reaming

Reamer Speeds & Feeds Calculator

Calculate reamer spindle speed and linear feed from SFM and IPR.

Open calculator → Spindle

Spindle Speed Calculator

Convert SFM and tool diameter to spindle RPM, or RPM back to SFM.

Open calculator → Shop

Machining Cost Calculator

Estimate setup, machine time, material, tooling and per-part cost.

Open calculator →

Core formula · inch units

How SFM is calculated

SFM = π × Diameter(in) × RPM ÷ 12RPM = SFM × 12 ÷ (π × Diameter)

The common 3.82 shortcut is an approximation of 12 ÷ π.

Workflow

From cutting data to machine settings

1

Get cutting data

Start with the toolmaker's recommendation for the exact tool, work material and operation.

2

Calculate spindle speed

Convert target SFM and actual cutting diameter into RPM.

3

Calculate feed

Use chip load or feed per revolution with RPM to determine the linear feed rate.

Machining reference

What is surface feet per minute?

Surface feet per minute (SFM) describes the linear speed at the cutting circumference. In milling, the relevant diameter is the cutting diameter of the tool. In turning, it is the machined workpiece diameter at the cut.

Why diameter changes RPM

At the same surface speed, a smaller diameter requires more revolutions per minute than a larger diameter. That is why SFM alone is not a spindle setting: it must be converted using the actual cutting diameter.

Important: A calculated RPM is not automatically a safe or optimal machine setting. Machine limits, workholding, tool geometry, stickout, coolant, rigidity and manufacturer guidance still matter.

Methodology & sources

Frequently asked

SFM calculator questions

How do I calculate SFM from RPM?

Multiply π by diameter in inches and RPM, then divide by 12. For a 0.5-inch diameter at 5,000 RPM, the result is about 654.5 SFM.

How do I calculate RPM from SFM?

Multiply SFM by 12, then divide by π times the cutting diameter in inches.

Is surface speed the same as spindle speed?

No. Surface speed is linear speed at the cutting circumference; spindle speed is rotational speed in revolutions per minute.

Should I use the nominal or effective cutter diameter?

Use the diameter where cutting actually occurs. On some profiled or angled tools this can differ from the nominal shank or major diameter.