Enter the mean free path length and the characteristic length into the Knudsen Number Calculator. The calculator will evaluate the Knudsen Number.

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## Knudsen Number Formula

The following two example problems outline the steps and information needed to calculate the Knudsen Number.

**Kn = FPL / CL **

Variables:

- Kn is the Knudsen Number ( )
- FPL is the mean free path length
- Cl is the characteristic length

## How to Calculate Knudsen Number?

The following steps outline how to calculate the Knudsen Number.

- First, determine the mean free path length.
- Next, determine the characteristic length.
- Next, gather the formula from above = Kn = FPL / CL .
- Finally, calculate the Knudsen Number.
- After inserting the variables and calculating the result, check your answer with the calculator above.

**Example Problem : **

Use the following variables as an example problem to test your knowledge.

mean free path length = 2

characteristic length = 5

Kn = FPL / CL ** **= ?