Centrifuge Speed Calculator — RPM to RCF (g-force)
Convert centrifuge rotor speed between RPM and RCF (relative centrifugal force, in × g). Enter the rotor radius and speed to find the RCF, or enter a target RCF to find the required RPM.
mm
RPM
× g
At 3,000 RPM, radius 100 mm
- 1
K × radius (1.118 × 10⁻⁶ × r)
1.118 × 10⁻⁶ × 100 = 0.00011182K = 4π² ÷ (g × 3 600 000) with radius in mm. - 2
RPM²
3,000² = 9,000,000 - 3
RCF = K × r × RPM²
0.00011182 × 9,000,000 = 1,006.4
How does this calculator work?
RCF = 1.118 × 10⁻⁶ × r(mm) × RPM². To find required RPM: RPM = √(RCF / (1.118 × 10⁻⁶ × r)). RCF scales with RPM², so doubling rotor speed quadruples g-force. Always use the same rotor radius the protocol specifies — different rotors produce different RCF at identical RPM.
Formula
How this is calculated
A laboratory centrifuge applies radial acceleration to samples. The relative centrifugal force (RCF) expresses this acceleration as a multiple of standard gravity (g = 9.806 65 m/s²). A sample at radius r (mm) spinning at N RPM experiences: RCF = (4π²/g) × r × (N/60)² = 1.118 × 10⁻⁶ × r × N². Because RPM² appears in the formula, doubling the rotor speed quadruples the RCF — small speed changes have large effects on sample pelleting.
The rotor radius is the distance from the centrifuge axis to the mid-point of the sample tube. Rotor specifications always list rmax and rmin; most protocols cite the average, ravg = (rmax + rmin)/2. Using the correct radius matters: at 10 000 RPM, rmax = 120 mm gives RCF ≈ 13 416 × g while rmin = 70 mm gives only ≈ 7 826 × g at the same speed.
The constant 1.118 × 10⁻⁶ is derived from 4π² / (g × 3600 × 1000) with r in mm and RPM in rev/min. Some sources quote 1.119 × 10⁻⁶ depending on the value of g used. The difference is negligible at typical rotor radii.
Frequently asked questions
RPM (revolutions per minute) is the rotation speed of the centrifuge rotor. RCF (relative centrifugal force, also called × g or g-force) is the actual acceleration the sample experiences, which depends on both RPM and rotor radius. The same RPM in a large rotor generates much higher RCF than in a small rotor.
RCF is portable across different rotors and centrifuge models: 10 000 × g is 10 000 × g regardless of which machine you use, as long as you set the correct RPM for your rotor radius. RPM-based protocols only replicate correctly on the original rotor.
Centrifuge rotors list rmax and rmin in the manual. Most protocols use ravg = (rmax + rmin) / 2. For pelleting assays, rmax (the tip of the sample tube) matters most. Always use the value specified in your protocol, or check the rotor specification sheet.
Also known as
TG we-Calculate Editorial Team. (2026). Centrifuge Speed Calculator — RPM to RCF (g-force) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/centrifuge-speed-calculator
TG we-Calculate Editorial Team. "Centrifuge Speed Calculator — RPM to RCF (g-force)." TG we-Calculate. 2026. https://we-calculate.com/calculator/centrifuge-speed-calculator.
TG we-Calculate Editorial Team, "Centrifuge Speed Calculator — RPM to RCF (g-force)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/centrifuge-speed-calculator
@misc{wecalculate_centrifuge_speed_calculator, title = {Centrifuge Speed Calculator — RPM to RCF (g-force)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/centrifuge-speed-calculator}}, year = {2026}, note = {TG we-Calculate} }
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