i know this probably sounds really stupid but how do i convert 20mm of gas into pascals?
Pa has units of [itex]N/m^2[/itex] thus you need a little more info to convert 20mm of gas to pascals.
[itex] p = h \rho g [/itex], when you use SI units in the RHS, P is in N/m^2. You need to know the density of the gas. g is the accelaration of gravity.
Separate names with a comma.