Most concrete calculators stop at cubic yards — useful if you're ordering a ready-mix truck, useless if you're standing in a hardware store aisle deciding how many bags to load into the cart.
How many bags of concrete do I need
This calculator converts the volume straight into bag counts for all three common premix sizes — 40 lb, 60 lb, and 80 lb — using each bag's manufacturer-published yield (0.30, 0.45, and 0.60 cubic feet of mixed concrete, the same numbers printed on the bag itself).
Concrete calculator cubic yards, for slabs and footings
Enter length, width, and thickness for a slab, footing, or wall and get the volume in both cubic yards (for ordering ready-mix) and cubic feet (for bag math), plus an estimated weight.
Post hole concrete calculator, with a hole-count multiplier
Setting fence posts? Switch to round mode, enter the hole's diameter and depth, and set how many holes you're filling — the volume and bag count scale automatically instead of you multiplying by hand.
