How much concrete your slab needs, in cubic yards and bags, with the working shown.
Add it to build one shopping list for your whole job.
Checked by Junayd
Order 1.36 cubic yards: that is 62 x 80 pound bags or 82 x 60 pound bags.
To find how much concrete you need, multiply length by width by thickness, all in feet. Divide by 27 for cubic yards, then add 4 to 10% extra. A 10 by 10 foot slab 4 inches thick needs 1.36 cubic yards with 10% extra, or 62 bags of 80 pound mix.
The working shows here once your sizes are filled in.
A concrete slab is normally 4 to 6 inches thick, depending on the load it carries (Quikrete). A sidewalk should be at least 4 inches thick. A 10 by 10 foot slab needs 1.36 cubic yards at 4 inches and 2.04 cubic yards at 6 inches, with 10% extra.
For a driveway or anything structural, check your local building code or ask a contractor. No manufacturer or code table we can cite gives a thickness for each use, so we don't either.
The choice between bagged concrete and ready-mix comes down to how much you need. One cubic yard is 45 bags of 80 pound mix, about 3,600 pounds to carry and mix by hand. Ready-mix arrives mixed by truck at about $110 to $195 a cubic yard delivered.
Many suppliers add a small-load fee below about 10 cubic yards, so ask yours. Bag prices, delivery fees and your own time vary too much for one honest break-even point. The concrete cost calculator prices both for your slab.
Order 4 to 10% more concrete than your measurements give, to cover contingencies, as the National Ready Mixed Concrete Association (NRMCA) advises. Sakrete advises 10% for every bagged estimate, which is where this calculator starts. On a 10 by 10 foot slab, 10% extra means 62 bags of 80 pound mix instead of 56.
NRMCA also advises against ordering well over the estimate.
Length 10 ft
Order 1.36 cubic yards: that is 62 x 80 pound bags or 82 x 60 pound bags.
Length 10 ft
Order 1.04 cubic yards: that is 47 x 80 pound bags or 63 x 60 pound bags.
Length 20 ft
Order 4.07 cubic yards: that is 184 x 80 pound bags or 245 x 60 pound bags.
A cubic yard is 27 cubic feet: a block 3 feet long, 3 feet wide and 3 feet deep. Multiply length by width by thickness, all in feet, then divide by 27 to get cubic yards.
One cubic yard of concrete covers 81 square feet at 4 inches thick, about 65 at 5 inches and 54 at 6 inches. That is 27 cubic feet divided by the thickness in feet, before any extra.
A typical ready-mix truck carries 9 to 11 cubic yards, a size set by road weight laws, according to the National Ready Mixed Concrete Association. Truck mixers range from 8 to 12 cubic yards.
Quikrete's method: dig about 7 inches deep, tamp 3 to 4 inches of gravel and build forms from 2x4 or 2x6 boards. Level the concrete, smooth it once the sheen has gone, then cut control joints and keep it damp for 3 to 5 days.
Each calculator uses the standard formula and the manufacturer's own figures, such as bag yields, and rounds up where running short would cost you a trip. Every step is shown. Cost ranges come from named surveys with the date we checked them. Spot something wrong? Tell us and we will fix it and note the change.