Measure your book around the spine from the edge of the front cover to the edge of the back cover. That is your width.
Measure your book cover
Then use your tape measure to measure the height of the book along the front cover vertically. This is your height.
If you want to keep things super simple you can of course cut one piece of fabric for your outer cover and just quilt it down to your batting.
Quilt Your Journal Cover
The flaps are the bits on the side that keep your book, journal or notebook inside your cover – sometimes called a book sleeve.
Attach the Journal Cover Flaps
Your folded edge for each flap should be facing each other and pointed towards the middle of your book cover.