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RCF to RPM Calculator (Centrifuge g-Force Conversion)
Enter the rotor radius, then either the speed or the g-force, and get the other one. Useful when a protocol gives ×g but your centrifuge only lets you set rpm.
Inputs
Convert
cm
r max: distance from the rotor axis to the tube bottom
×g
Results
- Speed
- 11,583 rpm
Formula
RCF (×g) = 1.118 × 10⁻⁵ × r (cm) × rpm²
rpm = √(RCF ÷ (1.118 × 10⁻⁵ × r))
Tip: Use r max, the distance from the rotor axis to the tube bottom. Results are rounded to whole numbers so you can enter them directly.
You got this step right, but a whole experiment has dozens of linked parameters. Change one dilution factor and everything downstream has to be recalculated. In Vara the parameters of your whole experiment are connected, so changing one recalculates the rest automatically. Manage 3 experiments for free.
FAQ
My protocol says 12,000 ×g but my centrifuge only takes rpm. What do I set?+
Find the rotor radius r (r max in cm, printed on the rotor or in the manual), then solve for speed: rpm = √(RCF ÷ (1.118 × 10⁻⁵ × r)). With r = 8 cm, √(12000 ÷ (1.118 × 10⁻⁵ × 8)) ≈ 11,583 rpm. If your centrifuge only steps in hundreds, use 11,600 rpm.
How do I find the rotor radius?+
Use the distance from the center of rotation to the bottom of the tube, listed as r max in cm. It is usually printed on the rotor or given in the centrifuge manual or on the manufacturer's site. Fixed-angle and swing-bucket rotors have different radii, so recalculate when you change rotors.
Why does the same rpm give a different g-force on another centrifuge?+
g-force scales with the radius and with the square of the speed. A larger rotor produces more force at the same rpm, which is why papers and kit manuals give ×g: it carries over to any centrifuge.
Roughly how many ×g is 3000 rpm?+
It depends on the rotor. A 15 cm swing-bucket rotor gives 1.118 × 10⁻⁵ × 15 × 3000² ≈ 1509 ×g, while an 8 cm rotor gives only about 805 ×g.
Do I need to change the spin time after converting?+
No. Once the g-force matches, keep the time from the protocol. If your centrifuge cannot reach the required ×g, a longer spin will not reliably make up for it, so use one that can.