When I moved furniture for minimal wage, we estimated the two densest things to move: textiles, then books. Bundles of rolled-up carpet were only beat by furniture. Large boxes of books might not seem bad until you have to move it a few times or the fatigue kicks in. All the boxes I’m using for books are smaller than around 12″ width, 12″ height, and 12″ depth. You never know who’ll give you a hand. Strong or otherwise.