Calculating How Many Bags of Concrete You Need

Last updated July 2, 2026

Concrete bag calculations convert the cubic yardage required for a project into the number of standard pre-mixed concrete bags needed, with a standard 80-pound bag yielding approximately 0.6 cubic feet of mixed concrete, meaning 45 bags are required to produce one full cubic yard, which contains 27 cubic feet. A small project requiring 3 cubic feet of concrete, such as a single fence post footing, needs approximately 5 bags of 80-pound mix, while a larger project like a 10 by 10 foot patio slab at 4 inches thick requires 33.3 cubic feet, or approximately 56 bags of pre-mixed concrete.

For projects requiring more than approximately 1 cubic yard, ready-mix concrete delivered by truck typically becomes more cost-effective and practical than bagged concrete, since the labor and physical effort of mixing dozens of individual bags becomes substantial at larger volumes, and most ready-mix suppliers have minimum order quantities around 1 cubic yard that align reasonably well with this breakeven point. Bagged concrete remains the more practical choice for smaller projects like fence post footings, small repairs, or projects where a ready-mix truck cannot access the site due to space constraints.

The concrete bag calculation uses the 45-bags-per-cubic-yard conversion factor for standard 80-pound bags, then compares the total bag count and labor required with ready-mix delivery for any project approaching 1 cubic yard or more. The breakeven point between bagged and ready-mix concrete typically favors ready-mix for larger projects despite the delivery minimum, given the substantial labor savings in mixing and the more consistent quality ready-mix delivery provides.