How much empty space should I leave for a barcode?
Leave a clear area near the lower portion of the back cover for the printer or distributor's barcode. Move the blurb and biography paragraphs upward when necessary so no text, face, logo, border detail, or ornament enters that area.
The Barcode Box option can help you reserve visible space while designing. If you add your own ISBN barcode image, keep it large enough to scan and avoid placing it over a busy or low-contrast background.