Centrifuge RPM to g-force (RCF) calculator
RCF (× g) = 1.118 × 10⁻⁵ × r × RPM², with r the rotor radius in centimetres; to go the other way, RPM = √(RCF / (1.118 × 10⁻⁵ × r)). For example, 10,000 RPM at a radius of 10 cm is 11,180 × g. Enter the speed or the g-force and the radius, or convert a protocol’s speed to the speed that gives the same g-force on your own rotor.
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At a glance
| Formula | RCF = 1.118 × 10⁻⁵ × r (cm) × RPM² |
|---|---|
| Solves for | RCF (× g), RPM, or the RPM for the same g-force on another rotor |
| Radius | cm or mm, from the axis to the sample; optional minimum and maximum |
| Sources | Klionsky 2026 (Autophagy); Harrison et al. 2023 (Cureus) |
| Runs in | Your web browser; nothing is uploaded |
| Price | Free, no account needed |
What it does
How to use the centrifuge RPM ⇄ g calculator
- Choose the directionRPM to × g, × g to RPM, or match a protocol written for another centrifuge.
- Enter the radiusThe distance from the centre of the rotor to the sample, from the rotor’s specification or measured, in cm or mm.
- Enter the speed or the forceType the RPM or the × g; the answer updates as you type. Add the minimum and maximum radius to see the force at the top and bottom of the tube.
How it works
RCF = 1.118 × 10⁻⁵ × r × RPM²
RPM = √(RCF / (1.118 × 10⁻⁵ × r))
Same g-force on another rotor: RPM₂ = RPM₁ × √(r₁ / r₂)
where RCF is the relative centrifugal force in multiples of Earth’s gravity (× g), r the radius in centimetres from the axis of rotation to the sample and RPM the speed in revolutions per minute. This is the relation given by Klionsky (Autophagy, 2026) and Harrison et al. (Cureus, 2023); the calculator reproduces Harrison et al.’s worked example (1000 × g at a 9 cm radius needs 3153 RPM). Because the force grows with the square of the speed, doubling the RPM gives four times the g-force (Bains et al., J Oral Biol Craniofac Res, 2023). The third line follows from setting the two forces equal.
The force is not the same throughout a tube: it is lowest at the top (minimum radius) and highest at the bottom (maximum radius), so methods should say which radius the g-force refers to; Miron et al. propose reporting the rotor dimensions, angle, RPM and time with the RCF (J Periodontol, 2019).
Worked example
RPM to × g. 10,000 RPM in a rotor with a 10 cm radius: RCF = 1.118 × 10⁻⁵ × 10 × 10,000² = 11,180 × g.
× g to RPM. For 1000 × g at a 9 cm radius: RPM = √(1000 / (1.118 × 10⁻⁵ × 9)) = 3153 RPM (the example in Harrison et al., 2023).
Matching a protocol. A protocol spins at 3000 RPM in a rotor with a 15 cm radius, which is 1.118 × 10⁻⁵ × 15 × 3000² = 1509 × g. On a rotor with an 8 cm radius the same force needs 3000 × √(15 / 8) = 4108 RPM; running it at 3000 RPM would give only 805 × g.
Frequently asked questions
How do I convert RPM to g (RCF)?
Multiply 1.118 × 10⁻⁵ by the rotor radius in centimetres and by the square of the RPM: RCF = 1.118 × 10⁻⁵ × r × RPM². At 5000 RPM and a 10 cm radius that is 1.118 × 10⁻⁵ × 10 × 25,000,000 = 2795 × g.
How do I convert g to RPM?
RPM = √(RCF / (1.118 × 10⁻⁵ × r)), with r in centimetres. For 1000 × g at a 9 cm radius, RPM = √(1000 / 0.00010062) ≈ 3153.
Is 10,000 RPM the same as 10,000 × g?
No. RPM is a speed and × g is a force, and the force depends on the radius as well. 10,000 RPM is 11,180 × g at a 10 cm radius but 5590 × g at 5 cm. Journals ask for × g, or the RPM together with the rotor, so that others can repeat the spin.
Which radius should I use?
The distance from the centre of the rotor to the part of the sample you care about, in centimetres. The rotor’s specification usually lists it; otherwise measure it. The force is smallest at the top of the tube (minimum radius) and largest at the bottom (maximum radius), so say which one you used.
How do I run a protocol on a centrifuge with a different rotor?
Keep the g-force, not the RPM. Work out the protocol’s × g from its speed and radius, then the RPM that gives that force on your rotor: RPM₂ = RPM₁ × √(r₁ / r₂). Use the “Match a protocol” mode.
Why does doubling the speed quadruple the force?
Because the force grows with the square of the speed: (2 × RPM)² = 4 × RPM². Halving the radius at the same speed halves the force.
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