RCF = 1.12 x Radius x (rpm/1000)²

Relative Centrifugal Force (RCF) is the term used to describe the amount of accelerative force applied to a sample in a centrifuge. RCF is measured in multiples of the standard acceleration due to gravity at the Earth’s surface (x g). This is why RCF and “x g” are used interchangeably in centrifugation protocols.

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Centrifugation is a process which involves the application of the centrifugal force for the sedimentation of heterogeneous mixtures with a centrifuge, and is used in industrial and laboratory settings. This process is used to separate two miscible substances, but also to analyze the hydrodynamic properties of macromolecules.^[1] More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture migrate towards the axis. Chemists and biologists may increase the effective gravitational force on a test tube so as to more rapidly and completely cause the precipitate (pellet) to gather on the bottom of the tube.

The general formula for calculating the revolutions per minute (RPM) of a centrifuge is

{\displaystyle RPM={\sqrt {g \over r}}},

where g represents the respective force of the centrifuge and r the radius from the center of the rotor to a point in the sample.^[4] However, depending on the centrifuge model used, the respective angle of the rotor and the radius may vary, thus the formula gets modified.

Source: Wikipedia.org

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How to convert centrifuge RPM to RCF of G-force

The force exerted on a particle in a centrifuge is a simple function of the rotation speed of the centrifuge and the radius of rotation. The actual equation is:

RCF or G-force= 1.12  x  R  x  (RPM/1000)²

 R is the radius of rotation measured in millimetres.

R can be measured at the top of the tube (Rmin), the middle of the tube (Rav) or the bottom of the tube (Rmax).  If your protocol does not specify, you can use chose but if you are trying to pellet something out, you should probably use Rmax as the pellet forms at the bottom of the tube.

Sedimentation

Particles in a suspension will settle in the bottom of a vessel over time, this is called sedimentation.  The particles fall to the bottom due to gravity, in the same way that herbs in a salad dressing settle at the bottom of the bottle.  This force is expressed as G.  Centrifugation increases the rate of sedimentation (i.e. accumulation of red and white bloods cells in the bottom of a blood tube) by spinning the blood samples and creating a centrifugal force that acts on the particles (in this case, red and white blood cells).

RPM stands for ‘revolutions per minute’.  This is how centrifuge manufacturers generally describe how fast the centrifuge is going (i.e. revolving).  The rotor, regardless of its size, is revolving at that rate.  The force applied to the contents, however, varies according to the size of the centrifuge as a larger centrifuge will have a longer radius and a smaller centrifuge will have a shorter radius.

For example, when revolving at 2000 RPM, a larger centrifuge with a longer radius length will spin samples at a higher g-force than a smaller centrifuge with a shorter radius length.

 source:clinfield.com