How to Calculate Machine RPM

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RPM is a function of surface speed.

In machining, surface speed represents the speed the cutter's outside edge travels. Use surface speed and the the cutter's size to calculate the rotation speed in revolutions per minute (RPM).


Step 1

Convert surface speed to feet per minute. To convert from meters per second, multiply by 196.85. For instance, if the surface speed is 2 m/s:

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2 * 196.85 = 393.7

Step 2

Multiply your answer by 4.

393.7 * 4 = 1,574.8

Step 3

Convert your cutter's diameter to feet. For instance, if your cutter measures 6in across:

6 / 12 = 0.5 ft


Step 4

Divide your answer from Step 2 by you cutter diameter in feet.

1,574.8 / 0.5 = 3,149.6

This is approximately 3,150 RPM.


"Surface speed" is also known as "cutting speed."

If you don't have a calculator handy, use your computer's calculator or a Google search bar.

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