Construction Calculators

Concrete Bag Calculator

Calculate how many bags of pre-mixed concrete (40 lb, 60 lb or 80 lb) are needed for a given volume.

Yield per bag —

Bags needed —

About the Concrete Bag Calculator

Pre-mixed concrete bags are a convenient option for small pours like fence posts, footings and small pads. Each bag size yields a different volume of finished concrete once water is added, so knowing the total volume you need lets you calculate exactly how many bags to buy.

Formula: Bags Needed = Volume (cu ft) ÷ Yield per Bag (0.30 for 40 lb, 0.45 for 60 lb, 0.60 for 80 lb)

Always round up and buy a few extra bags — running short mid-pour can ruin a monolithic finish, and unopened bags can typically be returned.