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 measured in RPM (revolutions per minute), but centrifugation protocols are written in RCF — relative centrifugal force, expressed as multiples of gravitational acceleration (× g). Converting between RPM and RCF requires knowing the rotor radius, creating a constant source of confusion in labs.
This calculator converts between RPM, RCF, and rotor radius using the standard formula RCF = 1.118 × 10⁻⁵ × r × RPM². Select what to solve for, enter your known values, and get instant conversions. Protocol presets cover common separations from cell pelleting to ultracentrifugation.
The RPM ↔ RCF reference table and lab protocol table, both adjusted for your rotor radius, make it easy to translate protocols across different centrifuges and set the correct speed for your specific rotor. Check the example with realistic values before reporting. Use the steps shown to verify rounding and units. Cross-check this output using a known reference case. Use the example pattern when troubleshooting unexpected results.
This calculator solves the universal lab problem of converting between RPM and RCF. Protocols from different labs or published papers specify RCF, but your centrifuge display shows RPM. Wrong conversions lead to incomplete separations or damaged samples.
Built-in protocol presets and rotor radius options save time and reduce errors when setting up cell biology, molecular biology, or clinical lab centrifugation protocols.
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.
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.