Calculate cubic yards of concrete, plus how many 60 lb or 80 lb bags you would need, for any slab, footing, or pad.
Estimates for planning only. Always confirm measurements and order a little extra for waste and cuts.
Concrete is ordered by the cubic yard (27 cubic feet). This calculator converts your slab, footing, or pad dimensions into yards and the number of 60 lb or 80 lb bags, so you order the right amount the first time.
Volume is length × width × thickness, with thickness converted from inches to feet, then divided by 27 to get cubic yards:
Cubic feet = length × width × (thickness ÷ 12)Cubic yards = cubic feet ÷ 27
An 80 lb bag of pre-mix yields about 0.6 cubic feet; a 60 lb bag yields about 0.45 cubic feet.
For small jobs (a few posts, a small pad), bagged concrete is convenient. But the bag count climbs fast: a single 10×10 four-inch slab needs roughly 56 eighty-pound bags. Once you're past about 1 cubic yard, ordering ready-mix from a truck is usually cheaper and far less work than mixing dozens of bags by hand.
Enter the length, width, and thickness of your slab, footing, or pad. Concrete is ordered by the cubic yard, which is 27 cubic feet, so the tool converts your dimensions the same way a supplier does. It multiplies length by width by thickness, converting the thickness from inches to feet first, to get cubic feet, adds a waste allowance (10 percent unless you change it in the waste field), then divides by 27 for cubic yards.
It also turns that volume into bag counts, because small jobs are often poured from bags. An 80 lb bag of pre-mix yields about 0.6 cubic feet and a 60 lb bag about 0.45, so the yardage becomes a straight bag count. The numbers climb fast: a 10 by 10 slab at four inches is roughly 56 eighty-pound bags before waste, which is why ordering ready-mix from a truck usually wins once you pass about one cubic yard.
This is a volume estimate, not an exact order. The tool does not know your real subgrade, thickened edges, or how much you will spill, so it covers those with that flat waste percentage instead, and you can raise or lower it to match your site. Leave the allowance in, and confirm the final load with your ready-mix supplier before pour day. If you are pricing the job for a customer rather than counting yards, a cost estimator is a better fit than this takeoff.
About 45 eighty-pound bags make one cubic yard, since each yields roughly 0.6 cubic feet and a yard is 27 cubic feet. Sixty-pound bags take about 60 per yard. Bagging much more than a yard by hand is hard work, so most crews switch to ready-mix past that point.
Yes, about 10 percent. Subgrade is never perfectly level, and running short in the middle of a pour means a cold joint or an emergency bag run. This calculator already folds a 10 percent waste allowance into its total unless you change it, so confirm the final load with your supplier rather than stacking more on top.