Centrifugal Force (RCF / g-force) Calculator
Convert between RPM (revolutions per minute) and RCF (relative centrifugal force in ×g). Find the rotor radius for your specific centrifuge and protocol.
Parameters
Distance from centre of rotor to bottom of tube
Result
| Parameter | Value |
|---|---|
| RPM | 3000 rev/min |
| Rotor radius (r) | 100 mm |
| RCF | 10062.0 ×g |
About Centrifugal Force & RCF
Centrifugation is one of the most fundamental techniques in biology and chemistry labs. Biological protocols specify the required force in relative centrifugal force (RCF, measured in ×g or g-force) rather than RPM, because RCF accounts for both rotor speed and the distance of the sample from the axis of rotation.
RCF vs. RPM
Two centrifuges spinning at the same RPM will generatedifferent forces if their rotor radii are different. Rotor radius is the distance from the axis of rotation to the bottom of the tube. By specifying RCF instead of RPM, protocols remain consistent across different centrifuge models with different rotor sizes. This is essential for cell separation, organelle isolation, nucleic acid purification, and protein precipitation.
The Equation
where RCF is in units of ×g, r is the rotor radius in mm, and RPM is revolutions per minute. The constant 1.118 × 10⁻⁵ arises from converting units (mm to m, minutes to seconds, gravitational acceleration to g).
Measuring Rotor Radius
The rotor radius must be measured from the centre of the rotor (the axis of rotation) vertically downward to the bottom of the sample tube when it is seated in the rotor bucket. Different rotor angles (fixed-angle, swinging bucket) and tube sizes result in different effective radii. Your centrifuge manual will specify the rotor radius, or you can measure it directly. A small error in radius measurement leads to a squared error in RCF, so precision matters.
Centrifugal Microfluidics
In microfluidic devices, centrifugal force is used to drive fluid motion, separate particles, and generate precise pressure gradients. Centrifugal microfluidics (lab-on-CD and centrifugal lab-on-chip platforms) exploit the strong radial acceleration to create capillary and viscous effects that enable mixing, pumping, and particle separation. Understanding RCF is critical for designing and operating these systems reliably.
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