Last updated October 2026 · Reviewed by the CostWise Lab team
How much concrete do I need?
Multiply length × width × thickness (all in feet) to get cubic feet, then divide by 27 to get cubic yards. A 10 × 10 ft patio that is 4 inches thick needs 33.3 cubic feet, or about 1.23 cubic yards. Order about 10% extra to cover uneven ground and spillage.
How many bags of concrete per cubic yard?
| Bag size | Yield per bag | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 cu ft | 90 |
| 60 lb | 0.45 cu ft | 60 |
| 80 lb | 0.60 cu ft | 45 |
Bags or ready-mix truck?
Bagged concrete makes sense for small jobs such as post holes, steps and pads under about 1 cubic yard. Beyond that, mixing 45+ heavy bags by hand is slow and the concrete may start setting before you finish. For larger slabs and driveways, a ready-mix delivery is usually faster and often cheaper. Many suppliers charge a short-load fee for small orders, so ask for the minimum.
Common slab thicknesses
- 4 inches: patios, walkways, shed bases.
- 5–6 inches: driveways and garage floors carrying cars.
- 6+ inches: heavy vehicles, RV pads.
Check local building codes for footings and structural work.
Methodology
Volumes are calculated with standard geometry; bag counts use typical manufacturer yields for bagged concrete mix.
column volume (cu ft) = π × (diameter ÷ 24)² × height
cubic yards = cu ft × (1 + extra) ÷ 27
bags = ⌈cu ft × (1 + extra) ÷ yield per bag⌉
Costs appear only if you enter your own local prices, because concrete prices vary widely between suppliers.
Sources
Frequently asked questions
How many 80 lb bags of concrete make a yard?
About 45. Each 80 lb bag yields roughly 0.60 cubic feet, and a cubic yard is 27 cubic feet.
How much concrete for a fence post?
A 10-inch-wide hole 3 feet deep holds about 1.6 cubic feet, roughly three 60 lb bags minus the space taken by the post.
How thick should a concrete patio be?
Four inches is standard for patios and walkways. Driveways usually need 5 to 6 inches.
Should I add extra concrete?
Yes. Ordering 5–10% extra covers uneven ground, spillage and form flex. Running short in the middle of a pour causes weak joints.