From the simulation, I can calculate how many particle collide with the wall per second,
Wih velocity and mass, the momentum can be calculated.

$\vec{F}=\frac{d\vec{P}}{dt}=\frac{d (m\vec{V})}{dt}$

and Pressure $P=\frac{F}{A}$  normal component of the momentum need to be calculated to from the pressure.