When choosing a centrifuge, RPM and RCF are specifications which must be considered. In centrifugation RPM is of course revolutions per minute. RCF is relative centrifugal force and the unit of measure is times the earths gravitational force at sea level or “x g”. RCF is dependent upon not only the RPM of the rotor, but the distance from the center of the rotor to the sample; this is the rotational axis. The length of the rotational axis will be different for each rotor used in the centrifuge. The formula for calculating RCF for a particular centrifuge rotor is:
where rcm is the distance from the center of the rotor to the sample in centimeters (rotational axis) and NRPM is the rotational speed of the rotor in revolutions perminute. Most manufacturers include charts with their centrifuge rotors which will give the RCF at any given RPM.