About the RPM to RCF Calculator
This RPM to RCF calculator converts a centrifuge’s rotational speed into relative centrifugal force — the g-force your samples actually feel — and works the other way to tell you what speed to set to reach a protocol’s “× g” value. Protocols should specify RCF rather than RPM because the same speed produces very different forces in rotors of different sizes.
It is for lab technicians, students and researchers moving a method between microcentrifuges, benchtop units and floor models. Enter the rotor radius from the manufacturer’s rotor sheet in centimetres, millimetres or inches; use the maximum radius (r max, tube bottom) to match the figure most protocols and centrifuge displays report.
The conversion is exact physics — RCF = r·ω²/g — so the only uncertainty is the radius you enter. Always stay within the rotor’s rated maximum speed and load.
How to use the rpm to rcf calculator
- 1Choose whether you are converting RPM to g-force or g-force to RPM.
- 2Enter the speed or the RCF your protocol calls for.
- 3Enter the rotor radius (r max from the rotor sheet) and its unit.
- 4Read the result, then confirm it is within the rotor’s rated maximum.
Formula and method
Relative centrifugal force is the centripetal acceleration r·ω² expressed as a multiple of standard gravity g = 9.80665 m/s². Converting revolutions per minute to radians per second (ω = 2π·RPM/60) and the radius to centimetres collapses the constants to (2π/60)² ÷ 9.80665 ÷ 100 ≈ 1.118 × 10⁻⁵.
Because RCF scales with the radius and the square of the speed, a sample farther from the axis feels more force at the same RPM, and a 10% speed increase raises the force by about 21%. Solving the same equation for RPM gives the speed needed for a target g-force.
- RCF
- Relative centrifugal force, multiples of g (× g)
- r
- Rotational radius, cm
- RPM
- Revolutions per minute
- ω
- Angular velocity, rad/s
Worked examples
3,000 rpm in a 10 cm rotor
RCF = 1.11824 × 10⁻⁵ × 10 × 3,000² ≈ 1,006 × g. The rotor turns at 2π × 3000/60 = 314.2 rad/s.
Speed for 16,000 × g in a microcentrifuge
RPM = √(16,000 ÷ (1.11824 × 10⁻⁵ × 8.4)) ≈ 13,051 rpm, which is why microcentrifuge protocols often pair ~13,000 rpm with ~16,000 × g.
4,500 rpm with radius in millimetres
A 155 mm radius is 15.5 cm, so RCF = 1.11824 × 10⁻⁵ × 15.5 × 4,500² ≈ 3,510 × g.
Frequently asked questions
How do you convert RPM to RCF?+
Multiply 1.118 × 10⁻⁵ by the rotor radius in centimetres and by the speed squared. A 10 cm rotor at 3,000 rpm gives 1.118 × 10⁻⁵ × 10 × 9,000,000 ≈ 1,006 × g.
What is the difference between RPM and RCF?+
RPM is how fast the rotor spins; RCF (× g) is the force samples feel. RCF depends on the radius as well as the speed, so protocols quote × g to be reproducible across centrifuges.
Which radius should I use: r max, r av or r min?+
Most protocols and centrifuge displays use r max, the distance to the bottom of the tube, where force is greatest. Use r av only if your protocol explicitly states average RCF.
Is RCF the same as g-force?+
Yes. RCF is the centripetal acceleration divided by standard gravity (9.80665 m/s²), so 1,000 × g means samples experience 1,000 times the acceleration of Earth’s gravity.
Why does a small speed change make a big difference?+
RCF depends on the square of speed. Increasing from 10,000 to 14,000 rpm (40% faster) almost doubles the g-force, because 1.4² = 1.96.