Centrifuge Rotor Calculator

• Relative centrifugal force (RCF): RCF (xg) = 1.118×10^-5 × r(cm) × RPM²
• Angular velocity: omega (rad/s) = 2π × RPM / 60
• Tip speed: v (m/s) = omega × r(m)
• Centripetal acceleration: a (m/s²) = omega² × r(m); g-force = a / 9.80665

1. What the rotor calculator solves

This tool links rotor radius and speed to relative centrifugal force (RCF). Enter RPM to estimate g-force, or enter a target RCF to find the needed RPM. It also reports angular velocity, tip speed, and tip acceleration, which help compare rotors and plan runs consistently. Use the precision control to match reporting needs, from quick checks to detailed documentation for quality systems and audits later easily.

2. Why radius matters in real tubes

RCF changes along the tube because r changes from the inner meniscus to the outer tip. Using minimum and maximum radius shows that spread. For example, at 12,000 RPM a rotor with r=8.0–12.0 cm produces about 12,871–19,306 xg, a difference near 50% across the sample length.

3. Core conversion used by manuals

Most centrifuge manuals use RCF = 1.118×10⁻5 × r(cm) × RPM². The constant embeds g and unit conversions. If you double RPM, RCF increases four times. If you increase radius by 20%, RCF rises 20% at the same RPM.

4. Speed planning from RCF targets

When you need a set g-force, solving for RPM prevents over-speeding. Suppose you want 13,000 xg at r=10.5 cm. The calculator returns roughly 10,540 RPM. If you mistakenly use r=8.0 cm, you would need about 12,060 RPM to reach the same force.

5. Tip speed and shear awareness

Tip speed is v = ωr and scales linearly with both RPM and radius. At 15,000 RPM and r=12.0 cm, tip speed is about 188.5 m/s. High tip speeds can increase shear for delicate cells, so lowering RPM while using a larger radius can keep RCF while reducing stress.

6. Safety limits and rated values

Rotors have maximum RPM and sometimes maximum RCF ratings. Exceeding either can damage the rotor and risk failure. Enter rated limits to trigger warnings. Always confirm limits for temperature, tube type, and corrosion history, because ratings can be reduced by wear or chemicals.

7. Using the results for reproducible protocols

Save the computed RPM, radii, and RCF values to document a protocol. Record whether RCF is quoted at average radius or at maximum radius. For multi-lab work, sharing RCF rather than RPM improves comparability across different rotor geometries and centrifuge models.

1) Should I enter average radius or min and max radius?

Use min and max when tube length is significant. The calculator shows RCF at both ends and at the average. If you only have one value from a manual, enter it as the average radius.

2) Why does RCF change so much for the same RPM?

RCF is proportional to radius and to RPM squared. Small RPM changes cause large g-force changes. Also, the sample experiences different radii along the tube, so the outer end always sees higher RCF.

3) Which radius should I use for protocols?

Many protocols quote RCF at the sample position or at maximum radius. Match what your rotor manual specifies. When sharing methods, include the radius value so others can reproduce the same force on different rotors.

4) Can I compare two rotors using tip speed?

Yes. Tip speed depends on radius and RPM, and it relates to shear and heating risk. Two rotors may deliver the same RCF but different tip speeds, so tip speed is a helpful secondary comparison.

5) What if my rotor has a rated maximum RPM but no rated RCF?

Enter the rated RPM and let the calculator estimate RCF at your radii. Use that as a planning limit, but still follow the manufacturer’s tables for temperature, tube type, and allowable load.

6) Do I need to account for temperature or viscosity here?

This calculator focuses on kinematics and g-force from geometry and speed. Temperature, viscosity, and density affect separation efficiency and run time, not the basic RCF conversion. Use your protocol or rotor guide to adjust time and conditions.