Centrifuge RCF (g) ↔ RPM Online Calculator

A protocol calls for “12,000 × g for 10 minutes,” but your centrifuge panel shows only rpm. These two numbers are not interchangeable — a rotor radius separates them.

Conversion formula:

RCF = 1.118 × 10⁻⁵ × r × N²

• RCF: relative centrifugal force, expressed as multiples of gravitational acceleration (× g)
• r: rotor radius in cm — distance from the axis of rotation to the bottom of the centrifuge tube
• N: rotational speed in rpm

To solve for speed: N = √( RCF / (1.118×10⁻⁵ × r) )

The most common mistake is choosing the wrong value for r. For any given tube, the distance from the tube bottom to the axis differs from the distance at the tube mouth, so manufacturers specify r_max (tube bottom) and r_min (tube mouth). For pelleting, the force at the tube bottom is what matters — use r_max. For a rough estimate, the rotor’s nominal maximum radius is sufficient; to reproduce a published result, consult the official rotor specification sheet for your instrument.

Typical benchtop centrifuge rotors fall in the 6–10 cm range; ultracentrifuge rotors span roughly 5–15 cm. Always verify against your instrument’s manual — the reference values on this page are for order-of-magnitude checks only.