Hi! This is Jon on behalf of Expert Village. In this video clip, we will be laying out our back piece. Now that we've rabbeted out our back and squared up the corners, we are ready to measure and lay out our back piece. Going back to our drawing, we have our back piece which will cover up the entire back section and it is going to be one full piece for each bookshelf. Now when you measure your back piece, you want to measure as close as you can to the top or bottom. If you measure it somewhere in the middle, your board could be bowed out and give you a wrong measurement. If I stick my tape measure on here and take a look, my size is 21 and just under a 1/4 inches. Now my other measurement was 69 1/2 inches so my overall measurement is 21 1/4 by 69 1/2. When you do measure for this, you want to make sure you measure from the inside of each groove. This will give you a very accurate reading. The material that I am going to be using for my back piece is a 1/4 inch veneer oak plywood. Now this is 4 ft. wide by 8 ft long and I should be able to get both back pieces out of this one piece for both of my oak bookshelves.