A step-by-step guide to making a basic hard cover for a multi-section book.
This one will have a bookcloth spine and paper sides.
This calculation will create a slight overhang of the cover boards - in this case 3mm - and a space at the spine edge to allow for movement and easy opening of the book. In this calculation I have allowed for a gap of 5mm at the spine but when you get more experienced at bookbinding, you could make this gap smaller, say 3-4mm.
Press the cloth at the spine to make a good shape: