The inside dimensions are 8.5″ wide x 6″ deep x 6″ high. The standard sign holder is 5.5″ above the box so an 8.5″x 11″ sign will fit in the sign holder but ½ of the sign will be behind the body of the box. The slot size is 4″ x 7/16″. This box is large enough that it can be used for drawings and to add a brochure pocket. The standard brochure pocket is 4″ x 4″ x 1″ and can be added at your request for an additional charge. An optional sign holder that is 8.5″ x 11″ above the box is also available. Please call for pricing and ordering for these options.