Concrete Forms Concrete has an extremely high density per cubic inch, making it extremely heavy with one square foot weighing nearly 150 pounds. Support is required both to take the weight of the concrete as well as to mold the concrete into the shape required. Due to the weight of material, strong materials are required for support and the most common and cost effective are metal and wood. The choice of form depends on the project, the amount of concrete required as well as the pressure that the form will be subjected to. For example, for work where the concrete will be poured flat with a supportive sub-base such as a driveway, the forms used range usually from 3 to 12 inches and are made of wood. However, when building a bridge, forms can reach 20 feet in height and are made from high quality steel to take the incredible weight of all that concrete. Wood Forms Wood forms can be either pre-manufactured or can be constructed on site, depending on the complexity of the project