How to calculate shrinkage for new green oak door?

I'm making a stable door from green /air dried oak. what is a standard calculation for accommodating the movement of the boards? Imagining to tongue and groove the boards together on a "Z" frame... should I fix the outside boards and let the movement happen between them with ample grooves? don't want to leave too much of a gap between the door and the frame...it will be warm and dry on the inside and exposed to the elements on the outside... any tips much appreciated! ta

It will expand & contract with the elements on a continual basis so I doubt there is any equation that calculates expansion & contraction as it dries & then absorbs moisture. I think it is just a question of making an educated guess.

The old style "Wood Butchers" used to leave the gap thickness of a penny between a wooden frame and wooden door, but then again they always returned after about three months to plane off the swelling of the door .