HesapHanem

CNC Spindle Speed Calculator

Enter your cutting speed, tool diameter and feed settings.

How it is calculated

The tool works in metric units. Spindle speed is RPM = 1000 × Vc ÷ (π × D) with cutting speed Vc in m/min and tool diameter D in mm. Table feed is feed = RPM × fz × z with feed per tooth fz in mm and number of teeth z, giving mm/min. The feed is calculated from the unrounded RPM and both results are rounded to whole numbers. Cutting speed and diameter must be above zero; feed per tooth and teeth may be zero (the feed is then 0 mm/min), but not negative. The result is a starting point from the tool maker's chart: it does not check machine maximum RPM, depth of cut, chip thinning or the rigidity of the setup. For inch tools, convert to mm and m/min first.

Worked example

A 10 mm three-flute end mill cutting at 200 m/min with 0.05 mm per tooth. RPM = 1000 × 200 ÷ (π × 10) = 200,000 ÷ 31.416 = 6,366 RPM. Feed = 6,366 × 0.05 × 3 = 955 mm/min. Both numbers are what you would type into the machine as S and F values, assuming it can reach that spindle speed.

Try this example →

Common mistakes

  • Entering the radius instead of the diameter, which doubles the RPM.
  • Using surface speed in feet per minute (SFM) in the cutting speed field; it expects metres per minute, and SFM is about 3.28 times larger.
  • Entering the feed per revolution instead of the feed per tooth, or forgetting to count the teeth, so the feed is several times too slow or too fast.
  • Using the full tool diameter for a ball nose or a chamfer cutter engaged only at its tip; the effective cutting diameter is smaller, so the real surface speed is lower than planned.
  • Accepting the RPM without checking it against the spindle limit; a small cutter in aluminium can calculate to far more than the machine can turn.

Sources

About this calculator

This calculator finds the metric spindle speed for a CNC machine using RPM = (Vc × 1000) ÷ (π × D), where Vc is the recommended cutting speed for the material and tool in meters per minute, and D is the tool diameter in millimeters — a formula derived directly from the fact that surface speed is the tool's circumference times its rotational speed. It also computes the table feed rate as RPM × feed-per-tooth (fz) × number of teeth (z), which determines how fast the machine advances the workpiece.

CNC machinists and manufacturing engineers use these two numbers together to set up a milling operation correctly: spindle speed too high for the material overheats and dulls the cutting edge, while a feed rate too low relative to spindle speed causes rubbing instead of cutting — both shortening tool life. Cutting-speed values (Vc) come from tooling manufacturer charts and vary widely by material, from roughly 20-40 m/min for hardened steel to 200+ m/min for aluminum.

Was this helpful?

You can pick up to 3 reactions.

Comments (1)

  • Editorial team

    When the calculated RPM is above what your machine can reach, run at the maximum and recompute the feed for that speed. The easy way here is to lower the cutting speed input until the RPM line matches your cap, because the feed line follows the RPM shown. Which materials or tool types would you like reference cutting speeds for?

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators