Sealing with two hard, flat surfaces

Imagine the following scenario:

There is a hollow steel cube. I cut the top facet off so that I get a box with a lid and then polish both cut surfaces so that geometry fits almost perfectly (no gaps are larger than 1/100 of a milimeter or so - or even smaller).
Then I close the box and introduce some pressurized air into it.

I press hard enough on the lid that all geometric faults are eliminated due to elastic properties of steel and also press hard enough to counter the force exerted by pressure.

Is there a way to calculate the amount of air leaking through the "gap" on account of surface roughness? I can specify Ra or Rz values, say Ra 0.2 - or any other value.


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