Convert between relative centrifugal force (x g) and rotor speed (rpm), using the maximum radius of your specific rotor.
Use the rotor's maximum radius (center of rotation to the bottom of the tube), not the average or minimum radius. This number is rotor-specific — look it up in your centrifuge or rotor manual. Do not assume it matches a different rotor of similar size.
Pick the direction you need, enter your rotor's maximum radius in the unit shown, and type in the value you know — either the target g-force or the rpm you plan to set. The other value updates instantly. Switch the radius unit with the toggle; the badge above the radius field always shows which unit is active so you don't feed mm into a cm-calibrated field by habit.
The most common error is reusing a radius from a different rotor because "it's the same brand" — radii vary between rotors even on the same centrifuge, and swapging rotors without updating this number gives you the wrong speed silently. Second most common: entering the radius in mm while the field is set to cm (or vice versa), which throws the rpm off by a factor of about 3.16. Also watch for confusing average radius (sometimes printed on rotor labels) with maximum radius — protocols almost always mean maximum radius when they specify RCF, and using average radius under-speeds your spin.