Concrete Calculator
Work out exactly how much ready-mix concrete or how many 60 lb / 80 lb bags you need for a slab, footing, or post hole.
Cubic yards
1.23yd³
Volume
33.3ft³
60 lb bags
75bags
80 lb bags
56bags
Ready-mix concrete is typically ordered by the cubic yard with a 5-10% overage. Bagged concrete counts assume standard yield (0.45 ft³ per 60 lb bag, 0.6 ft³ per 80 lb bag).
How the concrete calculator works
Concrete volume is a straightforward box calculation: length × width × thickness. The only trick is keeping your units consistent — this calculator takes length and width in feet and thickness in inches, then converts everything to cubic feet before dividing by 27 to get cubic yards (since 1 cubic yard = 27 cubic feet).
Formula: volume (ft³) = length × width × (thickness ÷ 12). Cubic yards = volume ÷ 27.
For bagged concrete, we divide total volume by the yield of a single bag — about 0.45 ft³ for a 60 lb bag and 0.6 ft³ for an 80 lb bag, per standard manufacturer spec sheets — then round up, since you can't buy a partial bag.
Frequently asked questions
At the standard 4-inch thickness, a 10x10 ft slab needs about 1.23 cubic yards of concrete, or roughly 74 bags of 60 lb pre-mix. Enter your exact dimensions above for a precise figure.
Ready-mix delivery is usually more cost-effective once you're above about 1 cubic yard (roughly a 9x9 ft slab at 4 in thick). Below that, bagged concrete mixed on-site is typically cheaper and more practical.
Suppliers generally recommend ordering 5-10% more than the calculated volume to account for spillage, uneven subgrade, and form deflection — most ready-mix trucks won't return for a small top-up.
Yes — volume scales directly with thickness. A driveway poured at 6 in instead of 4 in needs 50% more concrete for the same footprint, which is why thickness has its own input above.