While there are no concrete numbers to sufboards it's a good idea when you start to keep more foam in the board that you can fine tune in the end before glassing.
Aim for a 1/2" thick nose tip and a 5/8" tail tip thickness. Then foil your board for a nice flowing line from the nose to tail. Don't get caught up in the numbers too much. Water doesn't know numbers...
Here's more info on Foil from our Design Guide:
The change in thickness you notice when you view aboard from the side is referred to as foil. This thickness flow in most modern boards is smooth and even, without noticeable lumps or transitions. Foil determines to a great degree the overall volume of the board, how it flexes, the degree to which it can be flexed before it snaps, and whether the board is designed for long drivey turns or quick snaps. In general, thinner boards (2 3/8 inches thick or less at the thickest point) will be more flexy, harder to paddle, and less drivey… but more responsive. These boards are most suited for better surf, smaller or more advanced surfers, and strong paddlers. Thicker boards (2 1/2+ inches thick or more at the thickest point) will be less likely to snap but stiffer in terms of flex, will be easier to paddle due to increased buoyancy, and be more drivey. They will be more difficult to control in bigger surf, but work better in weak, small or slow waves because the added volume will allow them to catch waves easier and give the rider something to “push off of” when putting the board on a rail. A thinner board would have a tendency to sink under these conditions. Obviously, heavier and more powerful surfers require boards with more volume for flotation and to resist being pushed too deeply into the water and stalling on a hard turn.
While a trained eye can get a good feel for what the overall thickness flow is doing, and what it is intended for, by viewing from the side, the best way to quantify foil is by taking measurements along the length of the board using calipers. Measurements are most often taken at 12 inches from the nose and tail, 24 inches from the nose and tail, and at the wide point. Typically, boards are 1/8 to 1/4 inch thicker 12 inches from the tail than from the nose, and 1/16 to 1/8 inch thicker 24 inches from the tail than from the nose. The thickest point is typically found at the wide point. Boards designed for drive over responsiveness have their wide points and thick points ahead of center. Retro boards, single fins, classic longboards, and guns are good examples. These boards paddle better because the concentration of foam volume is under the chest when lying prone, and the center of the buoyant force is closer to the front foot when riding. Modern performance shortboards, however, have their wide and thick points behind center, which makes them inherently more difficult to paddle, but have a tighter turning radius. Rather than having the bulk of volume under the chest and front foot, the thick point back puts the concentration of foam between the surfers feet, better facilitating back-footed, rail-to-rail surfing.