QuickCheckToolsConcrete calculator
Work out how much concrete you need for a slab, footing or post holes, in cubic yards and in 80, 60 or 40 lb bags.
Bags of concrete per cubic yard
| Bag size | Yield per bag | 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 |
How far one cubic yard goes
| Slab thickness | Area covered by 1 cubic yard |
|---|---|
| 2 inches | 162 sq ft |
| 3 inches | 108 sq ft |
| 4 inches | 81 sq ft |
| 5 inches | 65 sq ft |
| 6 inches | 54 sq ft |
| 8 inches | 41 sq ft |
Questions
How much concrete do I need for a 10x10 slab?
A 10 x 10 foot slab 4 inches thick needs 33.3 cubic feet, which is 1.23 cubic yards. That is 56 bags of 80 lb concrete mix, or 75 bags of 60 lb. Add 5–10% extra for spillage and uneven ground.
How many bags of concrete are in a yard?
One cubic yard is 27 cubic feet. It takes 45 bags of 80 lb mix (0.60 cu ft each), 60 bags of 60 lb (0.45 cu ft each) or 90 bags of 40 lb (0.30 cu ft each).
How thick should a concrete slab be?
4 inches is standard for patios, walkways and shed bases. Driveways are usually 4–6 inches, and slabs carrying heavy vehicles 6 inches or more. Check local building requirements for structural work.
Should I buy bags or ready-mix concrete?
Bags are practical for small jobs such as post holes, steps and small pads, usually up to about one cubic yard. For larger pours, a ready-mix delivery is usually cheaper and gives a more consistent pour.
How much extra concrete should I order?
Most people add 5–10% to allow for uneven ground, spillage and form bulging. This calculator lets you add a waste allowance before the bags are rounded up.
How much concrete for a fence post?
Measure the hole diameter and depth. A 10-inch hole 3 feet deep holds 1.64 cubic feet, which is three 80 lb bags. The post takes up a little room, so this slightly overestimates, which is the safe side.
Bag yields are typical manufacturer figures for standard concrete mix (for example Quikrete). Check the yield printed on your bag, and follow local building requirements for structural work.