How to Convert RPM to RCF

By David Robinson
A centrifuge separates molecules within a solution.
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Centrifugation is a standard scientific process involving rotation. Revolutions per minute, or RPM, measures how frequently a rotor arm spins; however, the radius of the rotor also factors into the force exerted at the end of the rotor arm. To standardize the forces used on different centrifuges a different measurement, called relative centrifugal force (RCF), is used; this is calculated from the RPM and the radius of the rotor, and thus is a measurement independent of the equipment used.

Step 1

Determine the point in the test tube at which to calculate the RCF; measure the radius of the tube, in millimeters, at that point. Call this distance "r" and record it for later use.

Step 2

Substitute the values for rpm and r into the formula for Relative Centrifugal Force:

RCF = 1.12r (rpm/1,000)^2.

For example, with an rpm of 200 and an r value of 30, the formula becomes:

RCF = (1.12 x 30) x (200/1,000)^2.

Step 3

Reduce the equation to calculate the RCF value. Using the example in the previous step, the equation reduces to:

RCF = 33.6 x (0.2)^2

This further resolves to 1.1344. The resulting RCF is the rpm value converted to relative centrifugal force.

About the Author

David Robinson has written professionally since 2000. He is a Fellow of the Royal Geographical Society and the Royal Meteorological Society. He has written for the "Telegraph" and "Guardian" newspapers in the U.K., government publications, websites, magazines and school textbooks. He holds an honors Bachelor of Arts in geography and education and a teaching certificate from Durham University, England.