As a rule of thumb, we recommend that you use a 15mm margin on all edges except for the binding edge. The biding edge will require a slightly wider margin to leave space for the binding when printing your book. This prevents images and text from being lost in the fold when you open the book.
This is what your files will look like when the margins are applied correctly. As you can see, the inside edge or binding edge (left margin) has a slightly larger margin applied.
The inside edge margin sizes differ depending on your binding type:
Paperback Book Printing: 18mm on the binding edge. 15mm on the other edges.
Hardback Book Printing: 19mm on the top and bottom edge, 18mm for the binding edge and 15mm for the outside edge.
Coil Bound Book Printing: 18mm on the binding edge. 15mm on the other edges.
Booklet Printing: Set all margins to 10mm.
You can learn more about this in our Files and Formats section.