This is a shelf with square corners, 8" wide as a standard and a polished edge. It is .500" thick. We can make any size shelf that you need so don't hesitate to send us a request. If the width is too wide just put in the notes field the exact width that you need. The thickness of the shelf will depend on how heavy the object are that you wish to place on them. If the total weight is more than what we think the 1/2" will hold then we can make them out of 3/4" but in 95% of the case 1/2" will be fine. If you want 3/4" we have added those to the drop down menu both with brackets and without. We also sell the brackets that will hold your shelves if you need those also. You can see what they look like in the pictures for this product. We include 4 brackets with each shelf, two for the top and bottom of each side. We do this for safety reasons and to save whatever treasures that you will be putting on them from falling into your sink if you happen to put an object too close to the edge and possibly cause the shelf to flip. By putting a bracket on the top edge it locks the shelf in place. If your shelf is wider than your window frame let us know so we can drill the mounting holes in the brackets appropriately. Note: Shelves that are 37" and longer will have a clear piece of 1/4" acrylic that is 1.25" tall glued to the back bottom edge for support. Also be aware that if you order a shelf that is less than 6" wide we will add a strengthening piece as the width adds to the strength and when you make it less wide the strength is lessened. Please measure then subtract an 1/8" for the difference in tape measures and the lack of squareness in home construction. If you need a size that is not listed please purchase the next size up that is closest to your size and send us a message in the notes field of the exact length and width that you need. We do custom sizes daily and would be more than happy to accommodate your needs. Please be aware that custom cut orders take a little longer than standard sizes. Please note that custom cut orders are not cancelable or returnable unless of course there is a defect in the product. Thank you for your understanding. Thank you for shopping with us at PlasticMart.