depends, first measure the top rim to the bottom glass pane, and measure it from front to back (inside :D ) lets say its 23 and 5/8 inches... minus an inch for the bottom space in your bubble trap and make that one baffle. lets say you want to divide your skimmer area from everything else, make sure you have water to flowing into and out of this area most importantly, secondly make sure you make the baffle high enough to supply enough water for the skimmer to run with whichever water depth is recommended unless you get a HOB skimmer. and as for the other 2 baffles in the bubble trap, make one higher than the other, start them from the bottom of the tank and measure whatever feels comfortable to you but make sure you leave plenty of room in your sump for excess water so that if your power goes out, whatever water from your display drains will have enough room in your sump and not overflow causing a flood in your home. make sure the shortest baffle in your bubble trap is closest to your return pump, thats where your water flow should be going. This is how i built my sump basically but there are numerous ways to do it and maybe someone else will chime in with what design works best for them.