Concrete calculator
Enter your slab's length, width, and thickness, pick the bag weight your store sells, and get cubic yards plus the number of bags to buy. A table shows the same slab at 3 to 6 inches thick in 40, 60, and 80 lb bags. The 10 percent overage is optional, and bag counts always round up.
Slab dimensions
feet, or 12 ft 3 in
bags
Thickness series
Waiting for slab dimensions.
QUIKRETE publishes that all yields are approximate. Home improvement retailers carry similar disclaimers that calculations are estimates only. This page rounds bag counts up, never down, and shows leftover volume explicitly.
- Cubic yards
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- Bags
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- Leftover
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- Network requests
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- Our own script
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What you'll be carrying
Bagged concrete is heavy, and the count adds up fast. The 10 by 10 slab at 4 inches below takes 62 bags of 80 lb with the default overage. That's 4,960 lb of mix to load, haul, and lift. One cubic yard alone is 45 bags of 80 lb, or 3,600 lb. Choosing 40 lb bags halves the weight of each lift and doubles the number of bags to lift. Check what your vehicle can carry before you load up, or ask the store about delivery.
A 10 by 10 slab at four inches
Ten feet by ten feet by four inches is 1.235 cubic yards. Using the QUIKRETE 1101 yield of 0.60 ft³ per 80 lb bag, that is 56 bags before overage, and the leftover line shows the unused fraction of the last bag because counts round up, never down. Look at the five-inch row of the series table and the same footprint needs 77 bags of 80 lb with overage, 15 more than at four inches, without retyping anything.
Four inches is the common patio starting point, not a governing number. Load, sub-base, and the local building department decide thickness. How thick should a concrete patio slab be explains what that four-inch figure assumes, and why your building department has the final say.
Why a series table
Thickness is the variable most people are still deciding. The table repeats the same footprint at three, four, five, and six inches so you can compare bag counts without retyping dimensions. Forty, sixty, and eighty pound columns use QUIKRETE 1101 yields cited on the page.
What this page will not compute
Footings, columns, round slabs, curbs, and stairs are out. It handles rectangles only. Bag yields are for QUIKRETE 1101, and other brands' bags can yield a little more or less, so check the yield printed on the bag you buy. Sakrete's published 45 bags of 80 lb per cubic yard matches the figure here. For a large pour, ready-mix concrete is ordered by the cubic yard, so use the cubic yards line and talk to your supplier.
Questions
How many bags of concrete do I need for a 10x10 slab?
At 4 inches thick, a 10 by 10 slab is 1.235 cubic yards. That takes 56 bags of 80 lb concrete, or 62 with the default 10 percent overage. In 60 lb bags it's 75, or 82 with overage. Counts always round up, and the table above repeats your slab at 3 to 6 inches.
How many bags of concrete are in a cubic yard?
It's 45 bags of 80 lb, 60 bags of 60 lb, 90 bags of 40 lb or 40 bags of 90 lb, before any overage. A yard is 27 cubic feet. We divide that by the QUIKRETE 1101 yields of 0.60, 0.45, 0.30 and 0.675 cubic feet per bag. Sakrete's published 45 bags for 80 lb matches.
How thick should a concrete slab be?
Four inches is the usual starting point for a patio. Load, the ground underneath and your local building department decide the real number. How thick should a slab be explains what that 4 inch figure assumes.
How much extra concrete should I order?
The overage box starts at 10 percent. That's a trade convention Sakrete suggests, not a standard, so set it to 0 if you'd rather not. Because bags round up, the result also shows what's left in the last bag. For a 10 by 10 slab at 4 inches, that's 0.53 cubic feet.
Can it figure concrete for fence posts or sonotubes?
No. It only handles rectangular slabs, so round holes, footings and columns are out. If you already know the hole's volume in cubic feet, divide it by the bag yield (0.60 for an 80 lb bag) and round up. That's the same sum this page runs for a slab, before it adds the overage.
Are my dimensions uploaded?
No. The math runs in this tab. A share link keeps your slab size after the # in the address, and browsers don't send that part to any server.
Related tools
Thickness is not a bag-count question: how thick should a concrete patio slab be is the matching explainer. More material calculators live on the home project tools hub, including the mulch calculator and the flooring calculator.