Results are estimates for planning and ordering. Real quantities vary with how material is loaded, how moist it is, how much it settles and how uneven your ground is. Confirm quantities and product weights with your supplier before you order.
Calculators that touch on structure, such as rebar and retaining walls, give quantities only. They do not design anything. Slab reinforcement, footing sizes and walls taller than a few feet depend on local building codes and site conditions; check with your local building department or a licensed engineer.