How Many Bags of Concrete Do I Need

For small residential projects, purchasing premixed bags of concrete is often more economical than ordering a transit-mix truck. To avoid multiple trips to the supplier, builders must calculate the exact number of bags needed based on the project volume and bag yield.

Premixed concrete bags are sold by weight, with 60-pound and 80-pound bags being the standard sizes. Each bag size yields a specific volume of wet concrete when mixed with water:

• 80lb Bag: Yields approximately 0.60 cubic feet (0.022 cubic yards).
• 60lb Bag: Yields approximately 0.45 cubic feet (0.017 cubic yards).
• 40lb Bag: Yields approximately 0.30 cubic feet (0.011 cubic yards).

To find the total number of bags, divide the total volume in cubic feet by the yield of the selected bag size. For example, a 100-square-foot slab that is 4 inches thick requires 33.3 cubic feet of concrete. Using 80lb bags, the calculation is 33.3 divided by 0.60, which equals 56 bags. Verify these calculations on the concrete calculator before purchasing.

Aggregates and cement in pre-packaged bags can settle during transport. Mixing the contents of the bag thoroughly before adding water ensures a uniform consistency. Builders also track curing times with concrete curing strength charts to schedule form removal.

Using bags allows for precise portioning but requires significant physical labor. For projects exceeding 1 cubic yard (equivalent to 45 bags of 80lb concrete), ordering ready-mix delivery is generally recommended to ensure a continuous pour and prevent cold joints.