The best way to order the correct size coil for your job is to create a sample book, then measure the thickness before placing your order. This isn't always possible, so we've put together a chart based on 20lb. bond which should help you make the correct decision before you place your order. A general rule of thumb is to order the next largest size if you are stuck between two sizes. The difference in sheet capacity is fairly small between sizes and a larger size makes it much easier to turn the pages in your document. Please check out our Coil Diameter Guide to help you with your decision.  Coil Diameter Guide