Concrete Calculator
To find how much concrete you need, multiply the area by the thickness and divide by 27 for cubic yards. By the bag, an 80 lb bag of concrete mix yields 0.60 cu ft, a 60 lb bag 0.45 cu ft, a 50 lb bag 0.375 cu ft, and a 40 lb bag 0.30 cu ft. It takes 45 of the 80 lb bags to make one cubic yard.
4 in for most slabs and patios; footings and posts are deeper - use the round option for posts.
Add prices to estimate cost (optional)
Enter your measurements above to see how much concrete you need.
Slabs, footings, and posts
For a flat slab or patio, use the rectangle option with a thickness of about 4 inches. For a round footing or fence-post hole, switch to the round option and enter the hole diameter and depth.
We add a 10 percent waste allowance by default, which is standard for bagged concrete to cover spillage, uneven subgrade, and over-excavated holes. You can change it.
Bags or ready-mix?
Bagged mix is right for small jobs: posts, small pads, and repairs. Mixing many bags by hand gets slow fast. Once you approach roughly half a cubic yard (around 22 to 23 of the 80 lb bags), a ready-mix delivery is usually easier and often cheaper.
One cubic yard takes about 45 bags of 80 lb mix, 60 bags of 60 lb, 72 bags of 50 lb, or 90 bags of 40 lb.
Concrete coverage chart
One cubic yard = 27 cubic feet. Coverage = volume / depth.
Frequently asked questions
How many 80 lb bags of concrete make a yard?
45 bags. An 80 lb bag yields 0.60 cubic feet and a cubic yard is 27 cubic feet, so 27 / 0.60 = 45 bags.
How many 60 lb bags of concrete in a yard?
60 bags. A 60 lb bag yields 0.45 cubic feet, so 27 / 0.45 = 60 bags per cubic yard.
How much concrete do I need for a fence post?
Use the round option with the hole diameter and depth. A 4 inch post in a 10 inch wide, 24 inch deep hole needs roughly one to two 50 lb bags. Always round up.
Should I add extra concrete?
Yes. A 5 to 10 percent overage is standard to cover spillage and uneven ground. This calculator adds 10 percent by default.
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