G-Force Calculator (RCF)
Convert between a centrifuge's speed (RPM) and its relative centrifugal force (RCF, or g-force). Enter the rotor radius and the value you know to get the other.
How it works
Relative centrifugal force (RCF), also called g-force, is the force applied to a sample in a centrifuge expressed as a multiple of Earth's gravity. It depends on both how fast the rotor spins and how far the sample sits from the centre, using the relation RCF = 1.118 × 10⁻⁵ × r × N², where r is the rotor radius in centimetres and N is the speed in RPM.
Because RCF depends on the radius, two centrifuges running at the same RPM can apply very different forces. Protocols usually specify RCF (in ×g) rather than RPM so the result is reproducible across rotors — convert RPM → RCF to check your run, or RCF → RPM to set your machine from a published protocol.
Examples
- A 10 cm rotor at 10,000 RPM produces about 11,180 × g.
- To hit 15,000 × g on an 8 cm rotor you need about 12,950 RPM.
- Same RPM, larger radius → higher g-force.
Frequently asked questions
- What is RCF or g-force?
- Relative centrifugal force is the force on a sample in a centrifuge, measured as a multiple of gravity (×g). It reflects the actual force, unlike RPM.
- Why convert RPM to RCF?
- Because RCF depends on rotor radius, RPM alone isn't reproducible across machines. Protocols specify RCF so the same force is applied on any rotor.
- What radius should I use?
- Use the rotor's maximum radius — the distance in centimetres from the rotor centre to the bottom of the tube — unless your protocol specifies otherwise.
- What is the formula?
- RCF = 1.118 × 10⁻⁵ × r × N², where r is the rotor radius in cm and N is the speed in RPM. Rearranged, N = √(RCF ÷ (1.118 × 10⁻⁵ × r)).