Concrete volume
Cubic yards = length × width × thickness (ft) ÷ 27
Bags = cubic feet ÷ bag yield
A 10 × 10 ft slab 4 inches thick is 1.23 cubic yards, or 1.36 with 10% extra. That is 62 bags of 80 lb mix, so for a slab this size, ready-mix is usually the better choice.
Bag yields
| Bag | Yield | Bags per cubic yard |
|---|---|---|
| 80 lb | 0.60 cu ft | 45 |
| 60 lb | 0.45 cu ft | 60 |
| 40 lb | 0.30 cu ft | 90 |
Slab thickness
Walkways 4 inches, patios 4 inches, car driveways 4 to 5 inches, garage floors and truck driveways 5 to 6 inches.
The gravel base under a slab is covered by the gravel calculator.
How many 60 lb bags of concrete are in a yard?
60 bags. A 60 lb bag yields about 0.45 cubic feet and a cubic yard is 27 cubic feet. With 80 lb bags you need 45 per yard, and with 40 lb bags, 90.
How much concrete do I need for a fence post?
For a 4 × 4 post in a 10-inch hole 3 feet deep, plan about 1.4 cubic feet of concrete, which is two to three 80 lb bags. The hole holds about 1.6 cubic feet and the post takes up about 0.25 of that.
Frequently asked questions
How many 80 lb bags of concrete are in a yard?
45 bags.
How much concrete for a 10x10 slab?
1.23 cubic yards at 4 inches thick, or about 62 bags of 80 lb mix with 10% extra.
How thick should a concrete patio be?
4 inches over 4 inches of compacted gravel.
More landscape material calculators
Gravel Calculator
Tons, yards and bags by stone type.
Asphalt Calculator
Tons of hot mix for driveways and lots.
Cubic Yard Calculator
Any dimensions to cubic yards.
Mulch Calculator
Yards and bags for beds and trees.
Topsoil Calculator
Soil for lawns, beds and fill.
Dirt Calculator
Fill dirt in yards, tons and truckloads.