Centrifuge RCF Calculator: RCF = 4 pi^2 r N^2 / (3600 g)

How many times gravity a sample feels in a centrifuge.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose which quantity you want to find.

Enter the other values in the units shown.

The calculator gives the answer with the formula, the substituted numbers, and the answer in other units.

Formulas used

  • RCF = \frac{4\pi^2rN^2}{3600\,g}
  • N = \sqrt{\frac{3600\,g\,RCF}{4\pi^2r}}

Worked example

With the default numbers in the calculator above:

  1. The formula, arranged to find the relative centrifugal force: relative centrifugal force = 4 x pi^2 / (3600 x g) x radius from the axis to the sample x speed^2
  2. Put the values in (every value in its SI unit): relative centrifugal force = 4 x pi^2 / (3600 x g) x 0.1 x 4000^2
  3. The answer: relative centrifugal force: 1789.19 g

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: What do you want to find? Speed; Relative centrifugal force (leave it as it is if this is what you are finding) 1789 g; Radius from the axis to the sample (leave it as it is if this is what you are finding) 0.1 m.

  1. The formula, arranged to find the speed: speed = square root of ((relative centrifugal force) / (4 x pi^2 / (3600 x g) x radius from the axis to the sample))
  2. Put the values in (every value in its SI unit): speed = square root of ((1789) / (4 x pi^2 / (3600 x g) x 0.1))
  3. The answer: speed: 3999.79 rpm

Common questions

What is RCF?

The relative centrifugal force, the acceleration of the sample as a multiple of gravity.

How do I convert rpm to g?

Multiply the radius in metres by the square of the speed in rpm and by 1.118 times 10 to the minus 3 (about 4 pi squared over 3600 g).

Why does the radius matter?

The speed along the circle is higher at a bigger radius, so the force is higher at the same rpm.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any physics or laboratory text (centrifugation).

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