Size the concrete for your footings or piers. Choose the shape, enter the dimensions and how many you are pouring, and get the total volume plus the number of bags to buy.
Bag yields: an 80 lb bag makes about 0.6 cu ft, a 60 lb bag about 0.45 cu ft. Add about 10% extra for spillage and over-dig.
See the Deck Footing Chart and How to Pour Concrete.
Calculating concrete for footings
Footing concrete is figured by volume, then converted to bags or yards. For each footing, compute the volume from its shape — a rectangular footing is length × width × depth; a round pier is π × radius² × depth — then multiply by the number of footings. Divide total cubic feet by 27 for cubic yards, or by the bag yield (about 0.6 cu ft for an 80-lb bag) for bag count, and add 5–10% for waste and over-dig.
For more than about a cubic yard total, ready-mix is usually cheaper and easier than mixing dozens of bags by hand. Footings must also extend below the local frost line and meet size requirements set by the load and soil — this calculator handles the volume, but always confirm footing dimensions and depth against local building code, since they’re structural.