Its me again.
Based on EN12101-6:
P=((2*(100-Fdc)*(Wd-D))/(Da*Wd)
where:
Wd - door with (m)
Fdc - force needed to be applied at the door handle to overcome the inherent resistance of the door opening without a pressure differential applied to the door (N); Note: it is usually between 10 to 50N but please seek advise at the supplier of the door.
Da - door area (m2)
D - distance from the door handle center to the nearest vertical edge of the door.
I hope it helps.
Regards