This calculator will calculate the angle from amount angle milled on the head deck.
The angle is from the amount angle milled off.
The width is the surface that will be cut from the intake side to the exhaust side of the head.
(The widest part that would be milled)
The amount calculated would be the amount cut from the exhaust side of the head going to zero amount being cut on the intake side.
(which would give the degree which you want of the angle cut)
One aspect you need to remember is that the intake face of the head will also change by the degree you mill the head deck surface.
(if you angle mill 1º, the intake face will decrease 1º also at the intake face)