Enter the thermal diffusivity (m^2/s) and the mass diffusivity (m^2/s) into the Calculator. The calculator will evaluate the Lewis Number. 

Lewis Number Formula

Le = a / Dc


  • Le is the Lewis Number ()
  • a is the thermal diffusivity (m^2/s)
  • Dc is the mass diffusivity (m^2/s)

To calculate Lewis Number, divide the thermal diffusivity by the mass diffusivity.

How to Calculate Lewis Number?

The following steps outline how to calculate the Lewis Number.

  1. First, determine the thermal diffusivity (m^2/s). 
  2. Next, determine the mass diffusivity (m^2/s). 
  3. Next, gather the formula from above = Le = a / Dc.
  4. Finally, calculate the Lewis Number.
  5. 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.

thermal diffusivity (m^2/s) = 15

mass diffusivity (m^2/s) = 123