If you look through the side of the the tank you can measure it yourself..you'd want to deduct 1/16" off that measurement so you can fit them inside and have room to maneuver them while installing.
Ideally you'd want glass baffles and you'd install them using aquarium silicone. Ask to get them 'seamed' when you have them cut so that you have no sharp edges.
Are you asking what height they should be?..and are they going into this 10g tank?
Would also be good to know how many baffles you are adding and if this will be a fuge or a sump.
Very informative & it tells you how to determine what you need and how to measure for it.
If you have more questions after reading this inof, of course we'd be more than happy to help you out!
thanks for the info, in the end won't needed, i great MR member (Scion_TC2005, thank you dude!) donated a sump to me, won't need to make one from scratch at this time.....