# Converting RPM to g- force (RCF) and vice versa

g Force or Relative Centrifugal Force (RCF) is the amount of acceleration to be applied to the sample. It depends on the revolutions per minute (RPM) and radius of the rotor. It is relative to the force of Earth’s gravity.

A good and precise protocol for centrifugation instructs you to use the g force rather than RPMs because the rotor size might differ, and  g force will be different while the revolutions per minute stay the same. Unfortunately, many protocols are written in hurry and instructions are given in RPMs.Therefore, one  has to convert g force (RCF) into revolutions per minute (rpm’s) and vice versa.

Modern centrifuges have an automatic converter but older ones do not. There is a simple formula to calculate this; only it  takes some time to do the calculation. Meanwhile, your cells might die or the biochemical reaction will go on for three times longer than it should.

There are several ways to make conversion:

1. Use a website where you can select centrifuge model and rotor head

2. Use online converters

3. Use Nomogram (Nomograph)

4. Make the calculation yourself

1. The most precise way to make conversion is to use converters for a particular centrifuge and a rotor head. Companies provide the data. Here are the links to a resources online from where you can pick up the model and rotor:

Beckman, Sorvall or Thermo Scientific

Sorvall, Beckman and Eppendorff

BeckmanCoulter

Eppendorf

Thermo Fisher

Science Gateway might have some centrifuges that are not listed above.

2. Here are several links to converters on line:

Insilico

Hettich

Broken Symetry

EnCor Biotechnology

Insilicase

3.  Print and  use  Nomogram (a graphical calculator).They are available from the following :

BD Biosciences

University of Maryland Website

Eppendorf  has two versions A and B;  the second one has numerous calculation tips.

Optics Planet

4. The formula is always good to have in case your internet is down or the above links cease to exist.

g Force (RCF) = (rpm)2 × 1.118 × 10-5 × r

RPM = √[RCF/(r × 1.118)] × 1 × 105

g = Relative Centrifuge Force

N = Revolutions Per Minute (RPM)

I hope the above information will make your calculation easy.

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#### Nives Kovacevic

Nives is a Promega Technical Service Scientist. She was born and educated in Knin, Croatia, where she developed her love of science and music. After completing her Agronomy studies at University of Belgrade, Serbia, Nives was a high school teacher in her home town. After her teaching experience, she continued her graduate studies at Aristotle University of Thessaloniki, Greece. She then continued with post doctoral training at UW-Madison in maize epigenetics. Today Nives lives in Middleton, Wisconsin, with her husband and enjoys hiking, swimming and skiing in the nearby bluffs, lakes and hills. The warm society and rich cultural life of Madison is a perfect environment for them.

## 2 thoughts on “Converting RPM to g- force (RCF) and vice versa”

1. Eppendorf AG Germany produces Centrifuges-both refrigerated ‘n’ non-refrigerated with a touch key pad that has a key which can change the RPM to RCF or vice versa with touch of the key. The product catalog has RPM/RCF conversion furmula with table and many valuable information on its index for Biotechnologists

2. Hi Rajan,