What is the difference between RCF and RPM in centrifuges?

When selecting an appropriate centrifuge, one of the key points to consider is the maximum speed and if this meets your protocol. Centrifuges have two measures of speed, known as RCF and RPM, and whilst these may be used interchangeably they are in fact very different measurements.

RPM - Rotation per minute

Simply, this is how many times per minute the rotor will spin. This measure cannot be compared across different centrifuges as it does not specify the force being exerted and this will differ based on the radius on the centrifuge as explained below. If your method details RPM but you are using a different size centrifuge, you will want to convert it to RCF to ensure the same force is being used.  

RCF - Relative centrifugal force 

It is also known as g force and is a measure of the actual force being exerted. It is calculated using RPM and the radius of centrifugation (distance from the centre of the rotor to the bottom of the tube being spun). You can calculate it using the following equation: This measurement is translatable across different sizes of centrifuges and most protocols will detail what you require in RCF for this reason.   Camlab stock a range of centrifuges from leading manufacturers including Ohaus, Eppendorf and Sartorius, you can check them out here.

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