This are the covers for a book I’ve recently designed for an author. The superimposed lines are explained below.
The page size for your book
The size of your book is a matter of choice. I always recommend B Format for paperbacks as it is common in both the USA and UK.
Will depend on the number of pages and the thickness of the paper used. Your chosen printer/publisher will have a simple way of calculating this for you. This measurement is sometimes called the ‘bulk’ or ‘book block’ or simply the ‘spine width’. Allow your spine copy to have sensible wiggle room.
All suppliers should have a guide available to you. They will show a bleed line, a safe line and possibly a preferred ISBN position.
The bleed area (the bit around the edge shown in outside the red line here. It is what gets trimmed off when your book is bound. Your image or background colour needs to extend into this area so that no nasty little white edges showing after it’s trimmed.
Printing and trimming is a precise operation, but sometimes the paper wiggles a little in the machine, sometimes moisture in the air can stretch the paper, you simply can’t guarantee to be accurate to fractions of a millimetre. For these reasons you should always have anything important, be it image content or copy, within the ‘safe print’ area. So avoid the areas outside the yellow line if you want to guarantee that it’s viewable on the final version.
You will need an ISBN on your book if you want to sell through any conventional channel, be it online or a retail outlet. Some print houses will not only supply you with an ISBN at no cost (Amazon are one), but will also insist that it goes in a particular location.