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Concrete Calculator: Cubic Yards and Bags for Any Pour
Slabs, patios, driveways, footings, post holes, Sonotubes, steps and curbs, one pour or many. Get cubic yards for a ready-mix order, or how many 40, 50, 60 or 80 lb bags to buy.
Concrete Calculator
- Pour 1Typical: 4 in for patios and car driveways, 5–6 in for heavy trucks and RVs1.23 cu yd
Bags or a truck? Bags suit small jobs such as post holes, steps and small pads. For bigger slabs, ready-mix is usually easier and more consistent; ask your supplier about minimum orders and short-load fees.
Bag yields from the Quikrete Concrete Mix data sheet (80 lb ≈ 0.60 cu ft). 1 cubic yard = 27 cubic feet. Weight assumes about 150 lb per cubic foot.
How Many Bags of Concrete in a Yard?
Bag yields from the Quikrete Concrete Mix data sheet. Divide 27 cubic feet by the yield of one bag, and round up.
Source: Quikrete Concrete Mix (No. 1101) data sheet. Other brands are similar; check the bag.
| Bag size | Yield per bag | Bags per cubic yard |
|---|---|---|
| 80 lb | 0.6 cu ft | 45 |
| 60 lb | 0.45 cu ft | 60 |
| 50 lb | 0.375 cu ft | 72 |
| 40 lb | 0.3 cu ft | 90 |
Concrete Slab Chart (4 Inches Thick)
Common slab sizes, before adding extra for waste. For 6 inches, multiply by 1.5.
| Slab size | Area | Cubic feet | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 10 × 10 ft | 100 sq ft | 33.33 | 1.23 | 56 | 75 |
| 10 × 12 ft | 120 sq ft | 40 | 1.48 | 67 | 89 |
| 12 × 12 ft | 144 sq ft | 48 | 1.78 | 80 | 107 |
| 10 × 20 ft | 200 sq ft | 66.67 | 2.47 | 112 | 149 |
| 12 × 24 ft | 288 sq ft | 96 | 3.56 | 160 | 214 |
| 20 × 20 ft | 400 sq ft | 133.33 | 4.94 | 223 | 297 |
| 24 × 24 ft | 576 sq ft | 192 | 7.11 | 320 | 427 |
| 30 × 30 ft | 900 sq ft | 300 | 11.11 | 500 | 667 |
Concrete Volume Formulas
- Slab or footing: length × width × thickness.
- Round post hole or Sonotube: 3.1416 × radius × radius × depth.
- Steps: add each step as a block from the ground up: width × (rise × step number) × run.
- Curb and gutter: length × (curb height × curb depth + gutter width × flag thickness).
- Then: cubic feet ÷ 27 = cubic yards.
How Thick Should Concrete Be?
- Patios, walkways, shed pads: usually 4 inches.
- Driveways for cars and SUVs: 4 inches minimum (Concrete Network).
- Half-ton trucks, large RVs: 5 to 6 inches.
- Bagged mix: Quikrete Concrete Mix is made for pours 2 inches thick or more.
Local code, soil and loads decide the final design; ask your building department or engineer for structural work.
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Questions
How do I calculate how much concrete I need?
Multiply length × width × thickness, all in feet, to get cubic feet, then divide by 27 for cubic yards. A 10 × 10 ft slab 4 inches thick is 10 × 10 × 0.333 = 33.3 cubic feet, or about 1.23 cubic yards. Add about 10% for uneven ground and spillage.
How many 80 lb bags of concrete are in a yard?
About 45. An 80 lb bag of Quikrete Concrete Mix yields about 0.60 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.60 = 45 bags. With 60 lb bags (0.45 cu ft) it takes 60, and with 40 lb bags (0.30 cu ft) it takes 90.
How many bags of concrete do I need for a 10x10 slab?
At 4 inches thick, a 10 × 10 ft slab is 33.3 cubic feet: 56 bags of 80 lb, or 75 bags of 60 lb, before waste. With 10% extra, that is 62 bags of 80 lb. For a slab this size, ready-mix delivered by truck is often easier.
How thick should a concrete driveway be?
Four inches is the usual minimum for a residential driveway used by cars and SUVs. For heavier vehicles such as half-ton trucks or large RVs, 5 or 6 inches is often recommended. Patios and walkways are usually 4 inches.
How many bags of concrete for a fence post?
It depends on the hole. A 10-inch hole 3 feet deep holds about 1.6 cubic feet, so roughly three 80 lb bags, or four 60 lb bags, per post. Enter your hole size and the number of posts in the calculator.
How much does a cubic yard of concrete weigh?
About 4,000 pounds. Normal-weight concrete is roughly 150 pounds per cubic foot, and a cubic yard is 27 cubic feet.
Should I add extra concrete for waste?
Yes. Most estimators add 5–10% for uneven subgrade, form flex and spillage. Running short in the middle of a pour can leave a weak joint, so a little extra is cheaper than a second delivery.