Concrete calculator
Cubic yards and bags for a slab, a footing, post holes or a column.
A 12 × 10 ft slab 4 in thick needs 1.63 cubic yards of concrete with 10 % extra: 74 bags of 80 lb, or 1.75 yd³ of ready-mix.
Measure
You need
44.0 ft³ · 1.25 m³ · 10 % extra included
Your shopping list
Premixed bags
74 bags of 80 lb (36 kg)
or 98 of 60 lb · 147 of 40 lb · 5,920 lb to carry
Ready-mix truck
Order 1.75 yd³ ( m³)
Rounded up to the next ¼ yd³
Type your bag price and your price per cubic yard to see which is cheaper.
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How it is calculated
- Volume of the slab12 ft × 10 ft × 4/12 ft = 40.0 ft³
- Plus 10 % extra40.0 × 1.10 = 44.0 ft³
- Cubic yards44.0 ÷ 27 = 1.63 yd³
- Bags, rounded up44.0 ÷ 0.60 ft³ per 80 lb bag = 74 bags
Bags of concrete for common slabs
4 in thick, 10 % extra included. Driveways and slabs that carry a car are usually poured thicker: see the 6 in table.
| Slab | yd³ | 80 lb | 60 lb | 40 lb |
|---|---|---|---|---|
| 4 × 4 ft | 0.22 | 10 | 14 | 20 |
| 6 × 6 ft | 0.49 | 22 | 30 | 44 |
| 8 × 8 ft | 0.87 | 40 | 53 | 79 |
| 10 × 10 ft | 1.36 | 62 | 82 | 123 |
| 10 × 12 ft | 1.63 | 74 | 98 | 147 |
| 12 × 12 ft | 1.96 | 88 | 118 | 176 |
| 12 × 16 ft | 2.61 | 118 | 157 | 235 |
| 10 × 20 ft | 2.72 | 123 | 163 | 245 |
| 16 × 16 ft | 3.48 | 157 | 209 | 313 |
| 20 × 20 ft | 5.43 | 245 | 326 | 489 |
| 20 × 24 ft | 6.52 | 294 | 392 | 587 |
| 24 × 24 ft | 7.82 | 352 | 470 | 704 |
6 in thick
| Slab | yd³ | 80 lb | 60 lb | 40 lb |
|---|---|---|---|---|
| 4 × 4 ft | 0.33 | 15 | 20 | 30 |
| 6 × 6 ft | 0.73 | 33 | 44 | 66 |
| 8 × 8 ft | 1.30 | 59 | 79 | 118 |
| 10 × 10 ft | 2.04 | 92 | 123 | 184 |
| 10 × 12 ft | 2.44 | 110 | 147 | 220 |
| 12 × 12 ft | 2.93 | 132 | 176 | 264 |
| 12 × 16 ft | 3.91 | 176 | 235 | 352 |
| 10 × 20 ft | 4.07 | 184 | 245 | 367 |
| 16 × 16 ft | 5.21 | 235 | 313 | 470 |
How many bags make a cubic yard
| Bag | Yield per bag | Bags per yd³ |
|---|---|---|
| 40 lb | 0.3 ft³ | 90 |
| 50 lb | 0.375 ft³ | 72 |
| 60 lb | 0.45 ft³ | 60 |
| 80 lb | 0.6 ft³ | 45 |
| 90 lb | 0.675 ft³ | 40 |
Frequently asked questions
How many 80 lb bags of concrete make a yard?
45 bags. A cubic yard is 27 cubic feet and an 80 lb bag of QUIKRETE Concrete Mix yields about 0.60 cubic feet: 27 ÷ 0.60 = 45. With 60 lb bags it takes 60, with 40 lb bags 90.
How much concrete do I need for a 10 × 10 slab?
At 4 inches thick, a 10 × 10 ft slab is 33.3 cubic feet, or 1.23 cubic yards. With 10 % extra that is 1.36 yd³: 62 bags of 80 lb or 82 bags of 60 lb.
How many bags of concrete for a 12 × 12 slab?
88 bags of 80 lb (118 of 60 lb) for a 12 × 12 ft slab 4 inches thick, 10 % extra included. That is 1.96 cubic yards, so many people order 2.00 yd³ of ready-mix instead.
How many bags of concrete per fence post?
For a 10 in hole 24 in deep around a 4 × 4 post (3.5 in actual), 0.92 cubic feet: 2 bags of 80 lb or 3 bags of 50 lb per post. The post itself takes up part of the hole, so it is subtracted.
Is it cheaper to buy bags or ready-mix?
It depends on your local prices. 45 bags of 80 lb make one cubic yard, so bagged concrete costs 45 × the bag price per yard. Compare that with the ready-mix price per yard plus any delivery or short-load fee: type both prices in the calculator above and it does the comparison.
Why add 10 % for waste?
Forms bulge, the ground is never perfectly flat and some concrete stays in the mixer or the wheelbarrow. Running short in the middle of a pour leaves a weak joint, so most people round up. Set the extra to 0 % if you want the exact volume.