About Different Shelf Thicknesses for Kitchen Cabinets
In general, shelf thicknesses range from 1/2" to 3/4". The thicker 3/4" shelves are the preferable option based on their increased rigidity over thinner shelves.
3/4" Thickness for Cabinet Shelves 
Shelves that are 3/4" thick are the most ideal option because the thicker material will prevent the shelf from sagging, bowing or warping under the weight of whatever is placed on it. All of our cabinet shelves are 3/4" thick.
5/8" Thickness for Cabinet Shelves 
Many cabinet lines will use a 5/8" thick material for their shelves. For a shelf, it would be best to go for the thickest option as this is where all the weight will be. You don't want your winter's supply of canned goods wearing out your cabinets!
1/2" Thickness for Cabinet Shelves 
Once you start getting into the 1/2" range, you really begin sacrificing quality. You can see how much of a difference it is from 3/4" and that this thickness is more prone to any type of damaging or warping. This should definitely be avoided if you are looking for strong and durable cabinets.