Centrifuge RPM ↔ RCF (g-force) Calculator
By Santaji GadepatilinUpdated October 27, 2026
Lab protocols specify centrifugation in g-force (RCF), but centrifuges are set in rpm — and the conversion depends on the rotor radius. Using the right RCF makes results repeatable on any machine. This free centrifuge RPM ↔ RCF calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the centrifuge RPM ↔ RCF calculator
Enter the speed in rpm and the rotor radius. The RCF is calculated. To convert a protocol’s × g to rpm, press × on Speed and type the RCF.
Centrifuge RPM ↔ RCF formula
RCF = 1.118 × 10⁻⁵ × r (cm) × rpm²
Example
12,000 rpm with an 8.5 cm rotor:
RCF = 1.118 × 10⁻⁵ × 8.5 × 12,000² = 13,684 × g
RCF at common speeds
| rpm | Radius 6 cm | Radius 8 cm | Radius 10 cm | Radius 15 cm |
|---|---|---|---|---|
| 1,000 | 67 | 89 | 112 | 168 |
| 2,000 | 268 | 358 | 447 | 671 |
| 3,000 | 604 | 805 | 1,006 | 1,509 |
| 5,000 | 1,677 | 2,236 | 2,795 | 4,192 |
| 10,000 | 6,708 | 8,944 | 11,180 | 16,770 |
| 13,000 | 11,337 | 15,115 | 18,894 | 28,341 |
| 15,000 | 15,093 | 20,124 | 25,155 | 37,732 |
rpm from RCF
rpm = √(RCF ÷ (1.118 × 10⁻⁵ × r))
To get 1,500 × g in a rotor with a 10 cm radius: rpm = √(1,500 ÷ 0.0001118) ≈ 3,663 rpm. Press × on Speed in the calculator and type the RCF.
Why protocols use × g
Different centrifuges have different rotor radii, so the same rpm gives different forces. Always report and follow × g rather than rpm so results are reproducible.
Typical spins
| Task | Typical force |
|---|---|
| Pelleting mammalian cells | 200–400 × g, 5 min |
| Separating plasma from blood | 1,000–2,000 × g, 10–15 min |
| Pelleting bacteria | 3,000–5,000 × g |
| Microcentrifuge DNA spins | 12,000–16,000 × g |
| Ultracentrifugation | 100,000 × g and above |
Which radius?
Use the radius to the bottom of the tube (rmax) for the maximum force, or the average radius (rav) to compare rotors. The rotor manual lists both.
Frequently asked questions
Why use RCF instead of RPM?
The force on samples depends on both speed and rotor radius. RCF (× g) is the same on any centrifuge, so protocols specify it.
Where do I find the rotor radius?
In the rotor manual — use the maximum radius (rmax) measured from the centre to the bottom of the tube.
What speed gives 10,000 × g?
Press × on Speed and enter 10,000 as RCF. With an 8.5 cm rotor that is about 10,260 rpm.
How do I convert rpm to g?
RCF = 1.118 × 10⁻⁵ × radius (cm) × rpm². At 12,000 rpm and 8 cm, RCF ≈ 12,880 × g.
What radius should I use?
Use r_max (centre of rotation to the tube bottom) from the rotor manual unless your protocol says otherwise.