Sonotube Calculator

A sonotube calculator estimates the concrete needed to fill round cardboard forms used for deck footings, porch piers, fence posts, columns, and similar foundations. The calculation treats each form as a cylinder. Diameter is converted from inches to feet, divided by two to obtain radius, squared, and multiplied by pi and the form height. Multiplying that volume by the number of identical tubes gives the total cubic feet. Because ready-mix concrete is commonly sold by the cubic yard, the calculator also divides cubic feet by 27. Accurate measurements matter because a small diameter change produces a larger volume change. Diameter is squared in the cylinder formula, so an 18-inch tube requires substantially more concrete than a 12-inch tube of the same height. Measure the inside diameter of the form and use the actual filled height, including any portion below grade. If tubes have different dimensions, calculate each size separately and add the totals. The displayed weight uses a planning density of 145 pounds per cubic foot for normal-weight concrete. Actual density varies with aggregate, moisture, and mix design. The cost field is optional and multiplies the calculated cubic yards by a supplied material rate. It does not include short-load charges, delivery, pumping, reinforcement, excavation, forms, labor, taxes, or waste. Suppliers may impose a minimum order, while bagged concrete should be estimated using the yield printed on the bag. Always round an order upward according to the supplier's increment and include a practical allowance for uneven excavation, spillage, settlement, and overfilling. Five to ten percent is common for uncomplicated work, but field conditions can justify more. This result is a quantity estimate rather than structural design advice. Footing diameter, embedment depth, reinforcement, bearing capacity, frost depth, and concrete strength must follow approved plans and local requirements. Confirm utility locations before digging, brace forms securely, and check that dimensions remain correct before placement. For critical columns or heavily loaded footings, have a qualified designer verify the foundation. Used with measured dimensions and appropriate allowances, the calculator provides a fast basis for ordering concrete and comparing project costs.