14 inch diameter and 9.333 inch diameter. I added a photo to my stream which shows the dimensions. For the white pieces, just measure in place, they will vary depending how far apart you make the top and bottom boards. I think my post in between was about 6 or 7 inches tall. Yes they will be wider at the top. I used foam core board for the sides and glued white paper strips over them to hide the seams. Good luck!