Centrifuges are often advertised by maximum revolutions per minute, yet the force acting on a sample also depends on rotor geometry. Comparing RPM alone can lead to the wrong instrument or protocol settings.
RPM and RCF Are Different Measurements
RPM describes rotational speed. Relative centrifugal force (RCF), often written as ×g, describes acceleration relative to gravitational acceleration at a specified rotor radius. The same RPM can generate different RCF values in different rotors.
Why Rotor Radius Matters
For a radius expressed in centimeters, a common conversion is RCF = 1.118 × 10⁻⁵ × r × RPM². The relevant radius may be specified as minimum, average or maximum, so use the convention required by your protocol and rotor documentation. Do not reuse an RPM setting across different centrifuges without checking the resulting force.
Evaluate Rotor and Tube Compatibility
Check permitted tube sizes, adapters, rotor capacity, maximum rotor speed and sample type. Rotor approvals and tube ratings can impose lower limits than the centrifuge drive can reach. Only use manufacturer-approved combinations and follow balancing instructions.
Temperature and Safety Considerations
Refrigerated models may be needed for temperature-sensitive samples. Consider acceleration and braking profiles, containment requirements and the rotor maintenance schedule. Routine inspection for corrosion or damage is important because high-speed components are subject to significant stress.
Build a Shortlist
Compare laboratory centrifuges using required RCF, rotor, tube volume, throughput and temperature range instead of RPM alone.