Headroom is from the cockpit floor up to the bottom of the center bow. Width was measured at the center bow, up at the top, estimating the actual width across the vertical sections of the bow (inside edge to inside edge) - I did not have a tape long enough to stretch across the entire width, so measured from the center to the side, trying to account for the curve where the bow bends from horizontal to vertical.
But don't copy mine, or your bimini will be too long (front to back) and too high. From the looks of the one Paladin uses, mine is maybe a foot or more longer, and must be at least 6 in higher - and I cannot sail with mine unfolded (too high for boom to clear), nor can I properly even sail with it stowed (unless I lift the boom a bit higher than the main holds it, using the topping lift).