Shelf Layout site

Bookshelves. Being used as bookshelves too. John Armstrong - Track Planning For Realistic Operation, and Linn H Westcott - 101 Track Plans For Model Railroaders 3/4" plywood just sitting on shelf brackets. Manufacturer claims 55kg per 20cm (vertical) with a 75mm screw into a wooden stud. I've got 63mm screw into a wooden stud, and almost no faith in their claim, so I'll settle for 20kg between two brackets - i.e. my books.