Enter your slab size and thickness. You get cubic yards, bag counts for 80, 60 and 40 lb bags, and which way of buying concrete is cheapest for your job.
How to calculate concrete
Concrete is ordered by volume. Suppliers price it by the cubic yard, and a cubic yard is 27 cubic feet.
Cubic yards = cubic feet ÷ 27
Bags = cubic feet ÷ yield per bag
Worked example: a 10 × 10 patio, 4 inches thick
10 × 10 × 4 ÷ 12 = 33.3 cubic feet. Add 10% for spillage and uneven ground and you get 36.7 cubic feet, or 1.36 cubic yards. In 80-lb bags (0.60 cubic feet each) that is 62 bags.
Concrete needed for common slabs
Exact volumes with no extra added. Add 5–10% when you order.
| Slab | Thickness | Cubic yards | 80-lb bags |
|---|---|---|---|
| 10 × 10 ft patio | 4 in | 1.23 | 56 |
| 12 × 12 ft shed pad | 4 in | 1.78 | 80 |
| 10 × 20 ft patio | 4 in | 2.47 | 112 |
| 12 × 24 ft driveway section | 5 in | 4.44 | 200 |
| 20 × 20 ft slab | 4 in | 4.94 | 223 |
| 20 × 24 ft garage floor | 6 in | 8.89 | 400 |
Bag sizes and yields
| 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 |
What concrete costs in 2026
Ready-mix concrete delivered by truck typically runs about $160 to $195 per cubic yard in 2026, and the 2025 national average was close to $180 according to ConcreteNetwork. Orders smaller than a full truck often carry a short-load fee, and deliveries far from the plant or on weekends cost extra.
Bagged concrete works out to roughly double the price per cubic yard, but you pay no delivery or minimum-order fees. That is why small jobs (post holes, a small pad, under about 1 cubic yard) are usually cheaper with bags, while anything much over 1.5 cubic yards is usually cheaper and far less work with ready-mix. The chart in the calculator shows where your job falls.
If you hire a contractor, expect them to quote by the square foot instead: around $6.50 to $10.50 per square foot for a plain slab including labor, according to ConcreteNetwork’s 2026 figures.
How thick should a slab be?
- 4 inches: sidewalks, patios, shed floors.
- 5–6 inches: driveways and garage floors for regular cars and pickups.
- 6 inches or more: heavy trucks, RVs or equipment.
Local building codes and soil conditions can require more, so check with your building department for anything structural.
Frequently asked questions
How many 80-lb bags make a yard of concrete?
45 bags. Each 80-lb bag yields about 0.60 cubic feet, and a yard is 27 cubic feet.
How much extra concrete should I order?
5 to 10%. Uneven ground, form bulges and spills eat more than people expect, and running short mid-pour leaves a weak joint.
Is it cheaper to mix concrete myself?
For under about 1 cubic yard, usually yes. Above that, ready-mix delivery usually costs less and saves a lot of heavy labor.
How much does a yard of concrete weigh?
Roughly 4,000 pounds, about 2 tons. That is why bag jobs get heavy fast.
Sources: ConcreteNetwork.com concrete price guide (updated July 2026); standard manufacturer bag yields.
