Concrete calculator
Volume = length × width × thickness. A 10 ft × 10 ft slab, 4 in thick, takes about 1.23 cubic yards of concrete, or 56 bags of 80 lb.
- Checked on thousands of cases
- Sources: QUIKRETE
- Updated November 5, 2026
Optional, printed on the bag
Concrete needed
33.3 ft³ · 0.94 m³
Pre-mixed bags
- Bag of 40 lb (18.1 kg)112 bags
- Bag of 50 lb (22.6 kg)89 bags
- Bag of 60 lb (27.2 kg)75 bags
- Bag of 80 lb (36.2 kg)56 bags
- Bag of 90 lb (40.8 kg)50 bags
Approximate yields of QUIKRETE Concrete Mix. For another brand or bag size, enter the yield printed on your bag.
Quick challenge
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How it works
Formula: Volume = length × width × thickness
For a slab, the calculator multiplies the length, the width and the thickness. For round holes or columns (for example fence posts or tube forms), it uses the area of a circle, π × radius², times the depth and the number of holes. You can add a margin for an uneven ground or spills. The number of bags divides the volume by the yield of one bag, rounded up: the yields shown are those published by QUIKRETE for its Concrete Mix, for example about 0.60 ft³ (17 L) for an 80 lb bag. For another product, enter the yield printed on your bag.
Bags of QUIKRETE Concrete Mix by volume
| Volume | 40 lb | 50 lb | 60 lb | 80 lb | 90 lb |
|---|---|---|---|---|---|
| 0.25 yd³ | 23 | 18 | 15 | 12 | 10 |
| 0.5 yd³ | 45 | 36 | 30 | 23 | 20 |
| 1 yd³ | 90 | 72 | 60 | 45 | 40 |
| 2 yd³ | 180 | 144 | 120 | 90 | 80 |
| 3 yd³ | 270 | 216 | 180 | 135 | 120 |
10 ft × 10 ft slab by thickness: volume and bags
| Thickness | Volume | 40 lb | 50 lb | 60 lb | 80 lb | 90 lb |
|---|---|---|---|---|---|---|
| 3 in | 0.93 yd³ | 84 | 67 | 56 | 42 | 38 |
| 4 in | 1.23 yd³ | 112 | 89 | 75 | 56 | 50 |
| 5 in | 1.54 yd³ | 139 | 112 | 93 | 70 | 62 |
| 6 in | 1.85 yd³ | 167 | 134 | 112 | 84 | 75 |
Frequently asked questions
How much concrete do I need for a slab?
Multiply length × width × thickness in the same unit. 10 ft × 10 ft × 4 in (0.333 ft) = 33.3 ft³, or 1.23 yd³ (1 yd³ = 27 ft³).
How many bags of concrete per cubic yard?
Divide 27 ft³ by the yield of the bag. With QUIKRETE Concrete Mix, an 80 lb bag yields about 0.60 ft³, so 45 bags per cubic yard; a 60 lb bag about 0.45 ft³, so 60 bags.
How do I calculate concrete for a post hole?
Volume = π × (diameter ÷ 2)² × depth. An 8 in hole, 36 in deep holds about 1,810 in³, or 1.05 ft³: two 80 lb bags with the yields above.
Should I add extra concrete?
An uneven base, a form that bulges or spills all consume more than the theoretical volume. Enter the margin you want in the 'Margin' field.