Convert centrifuge speed in RPM to relative centrifugal force (× g), or work back from a protocol's × g to the RPM your rotor needs. Add a second radius to match runs between different rotors.
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Convert
Distance from the rotor axis to the sample (use r max for the bottom of the tube)
RPM
× g
Optional: match another rotor
Finds the RPM that gives the same RCF on a rotor of this radius
Top of the liquid column; shows the RCF range across the tube
Enter your values to see the result.
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How to use the Centrifuge RPM to RCF Calculator
Choose a direction: RPM to RCF, or RCF to RPM.
Enter the rotor radius from the rotor manual (r max is usual).
Enter the speed or the × g from your protocol.
Optionally add a second radius to convert a protocol to another rotor.
Copy the result or download the RPM-to-RCF table.
RPM to RCF formula
Relative centrifugal force is the centripetal acceleration of a sample, r × ω², divided by standard gravity. Writing ω = 2π × RPM ÷ 60 and expressing r in centimetres gives the familiar lab formula:
RCF = 1.118 × 10⁻⁵ × r(cm) × RPM²
RPM = √(RCF ÷ (1.118 × 10⁻⁵ × r(cm)))
Same × g on another rotor: RPM₂ = RPM₁ × √(r₁ ÷ r₂)
Example: a fixed-angle microcentrifuge rotor with r = 8.4 cm at 13,000 RPM gives 1.118 × 10⁻⁵ × 8.4 × 13,000² ≈ 15,880 × g. Because speed is squared, doubling the RPM multiplies the force by four.
RCF at common speeds
RPM
r = 5 cm
r = 8.4 cm
r = 10 cm
r = 16 cm
1,000
56
94
112
179
3,000
503
846
1,007
1,611
5,000
1,398
2,349
2,796
4,474
10,000
5,592
9,395
11,185
17,896
15,000
12,583
21,139
25,166
40,265
Values are × g, rounded. Always check your rotor's maximum rated speed, and never exceed it.
Practical tips
Balance tubes by mass, placing equal tubes directly opposite each other.
For swing-bucket rotors, r changes with tube type and adapter; use the value for your bucket and tube combination.
Pelleting efficiency also depends on time, temperature and path length, so convert run time with the rotor's k-factor when switching between very different rotors.
Frequently asked questions
What is the formula to convert RPM to RCF?
RCF = 1.118 × 10⁻⁵ × r × RPM², with r the rotor radius in centimetres. It comes from RCF = rω²/g with ω = 2π × RPM / 60 and g = 9.80665 m/s².
How do I convert RCF (× g) to RPM?
Rearrange the formula: RPM = √(RCF / (1.118 × 10⁻⁵ × r)). For 15,000 × g on a rotor with r = 8.4 cm that is about 12,640 RPM.
Why is RCF better than RPM in a protocol?
The force on a sample depends on both speed and radius, so the same RPM gives different × g on different rotors. Quoting × g (and time) lets anyone reproduce the run on their own centrifuge.
Which radius should I use?
Rotor manuals list r max (axis to the bottom of the tube), r min and sometimes r avg. Most protocols use r max. For a swing-bucket rotor, measure with the buckets swung out horizontally.
How do I match a run on a different rotor?
Keep RCF the same: RPM₂ = RPM₁ × √(r₁ / r₂). A larger rotor needs a lower RPM for the same × g. Enter the second radius in the optional field to get the value.
Is RCF the same as g-force?
Yes. RCF is the centripetal acceleration on the sample expressed as a multiple of standard gravity, written × g. 10,000 × g means 10,000 times Earth's gravitational acceleration.
Are all the tools on FreeToolCabin tested for quality and accuracy?
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