Bookshelf Calculator — Materials & Dimensions

For 18mm plywood, keep unsupported spans under 750mm for book-loaded shelves (you can reach ~800mm if you glue a solid hardwood front edge-band to stiffen the shelf). For 25mm solid hardwood, spans up to 1000mm are acceptable. 18mm MDF sags noticeably over 600mm and is best avoided for heavy books. For longer shelves, add a vertical divider or use a thicker material. A centre support can effectively double the allowable total width.

Birch plywood (18mm) is the most popular choice — it is strong, stable, and finishes well. Solid hardwood (25mm) is strongest and most attractive but heavier and more expensive. MDF is cheapest but weakest and heaviest; best for painted shelves under 600mm span.

Standard paperback books need 200-230mm between shelves. Hardback books need 260-300mm. Art books and large formats need 320-380mm. A mix of spacing works well — taller gaps at the bottom and shorter gaps at the top. Adjustable shelf pins on a 32mm grid give the most flexibility.

A back panel (typically 3mm plywood or 6mm MDF) adds significant rigidity and prevents the bookcase from racking (going out of square). Without a back panel, you need diagonal bracing or a very rigid joint system. The back panel also prevents books from falling behind the shelf.