Convert between RPM and RCF (× g) for centrifuges. Calculate required RPM from g-force or compute RCF from speed and rotor radius.
Centrifuge speed is usually shown as RPM, but lab protocols are often written in RCF, or relative centrifugal force, which is the actual acceleration experienced by the sample. Converting between the two depends on rotor radius, so the same protocol can require different RPM on different machines.
This calculator converts between RPM, RCF, and rotor radius using the standard relationship RCF = 1.118 × 10^-5 × r × RPM^2. Enter the values you know, choose what you want to solve for, and it will return the matching centrifuge settings.
Protocol presets and reference tables make it easier to translate a published RCF into the RPM your rotor needs, or to see how strongly a given spin will act on the sample.
Centrifuge protocols are easy to misapply when the paper reports RCF but the instrument shows RPM. The radius of the rotor changes the actual force, so a correct conversion is the difference between a usable separation and a spin that is too weak or too aggressive.
Putting RPM, RCF, and rotor radius on the same page helps with protocol transfer, rotor selection, and quick checks before you run a sample.
RCF = 1.118 × 10⁻⁵ × r × RPM². RPM = √(RCF / (1.118 × 10⁻⁵ × r)). r = RCF / (1.118 × 10⁻⁵ × RPM²). Where r is the rotor radius in centimeters.
Result: 1,413 × g
At 3,000 RPM with a swinging-bucket rotor (14.0 cm radius), the sample experiences 1,413 times gravitational acceleration. This is suitable for cell pelleting and serum separation protocols.
Differential centrifugation separates cellular components by successive spins at increasing g-force. The first spin at 300 × g pellets intact cells but leaves organelles in the supernatant. The 10,000 × g spin pellets mitochondria and lysosomes. The 100,000 × g ultracentrifuge spin brings down microsomes and ribosomes.
Fixed-angle rotors pellet particles against the tube wall, resulting in faster sedimentation but compacted pellets. Swinging-bucket rotors pellet to the tube bottom, producing loose pellets ideal for gradient separations. The effective radius is different for each type.
Sucrose, cesium chloride, or Percoll gradients allow separation by density rather than just size. Isopycnic (equilibrium) centrifugation spins samples long enough that particles band at their buoyant density. Rate-zonal centrifugation separates by sedimentation rate in a short spin.
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RCF describes the actual force on the sample, which determines separation effectiveness. Different centrifuges with different rotor radii need different RPM to achieve the same RCF, making RPM non-transferable between instruments.
Measure from the center of the rotor (axis of rotation) to the bottom of the sample tube or the furthest point the sample reaches. Check your rotor manual for the exact specification — it varies between fixed-angle and swinging-bucket designs.
RCF (relative centrifugal force) and × g are the same thing: a dimensionless ratio comparing centrifugal acceleration to gravitational acceleration (9.81 m/s²). "300 × g" and "RCF 300" are interchangeable.
The squared relationship means small RPM changes have large effects on g-force. Increasing from 3,000 to 4,000 RPM (33% increase) raises g-force by 78%. This is why accurate RPM is critical for reproducible separations.
Only if your centrifuge can handle that RPM safely. Always check maximum RPM ratings for your specific rotor. Using a smaller-radius rotor requires higher RPM for the same RCF, which may exceed limits.
The k factor is a measure of pelleting efficiency that accounts for rotor geometry. A lower k factor means faster pelleting. It is calculated from the maximum and minimum radii and the maximum RPM of the rotor.