🌀 Centrifuge RPM ↔ RCF Calculator
Convert between rotor speed (RPM) and relative centrifugal force (RCF, ×g) using your rotor radius.
Frequently asked questions
Is RCF the same as RPM?
No. RPM is how fast the rotor spins (revolutions per minute); RCF (relative centrifugal force, ×g) is the actual force applied to your sample, which depends on both RPM and the rotor's radius. Two centrifuges at the same RPM can apply very different RCF if their rotor radii differ.
Which radius should I use — r_min, r_avg, or r_max?
Most published protocols specify RCF using r_max (center of rotation to the bottom of the tube), which gives the highest force experienced by the pellet. Use r_max unless your protocol specifies otherwise.
Why does my result differ slightly from my centrifuge's built-in calculator?
Small differences can come from rounding or from using r_avg instead of r_max. Always check your rotor manual for the exact radius value it uses.
Accuracy & how this is derived
Derivation: RCF is derived from the physics of circular motion: centrifugal acceleration a = ω²r, converted to units of standard gravity (g = 9.80665 m/s²) and RPM instead of angular velocity, giving the constant 1.118×10⁻⁵ (with r in cm).
Validated against: Standard centrifugation physics formula used across biochemistry and molecular biology lab manuals (e.g. Sambrook & Russell, Molecular Cloning).
⚠️ For educational and research support only — verify critical results independently before use in regulated, clinical, or publication-bound work.
✔ Last updated: July 2026 · Report an error
RPM vs RCF: why the difference matters
Centrifuge protocols are often written in RCF (×g) because it reflects the actual force applied to a sample regardless of which centrifuge or rotor is used, whereas RPM alone depends on the specific rotor's radius. Converting between the two lets you reproduce a protocol written for one rotor on a different centrifuge. A common mistake is assuming RPM values are interchangeable between instruments — always convert to RCF first when following a published protocol on unfamiliar equipment.