Concrete calculator
A 10 × 10 ft slab 4 inches thick takes 33.33 cu ft of concrete, or 62 bags of 80 lb mix once you add 10% extra. Pick the shape you are pouring and enter its size.
Slab patio, shed base, walkway
Footing a rectangular trench or pad
Round column post holes, tube forms
For post holes, the post itself takes up some room, so this slightly overestimates.
Steps solid concrete stairs
Each step is counted as a solid block down to the ground. A top landing adds a platform as tall as all the steps.
Bags and extra
Sakrete's estimating guide says it is "always a good idea to add 10%". Uneven ground or a thicker edge may need more.
How the bags are counted
- Volume in cubic feetLength × width × thickness, with the thickness in feet: 10 × 10 × (4 ÷ 12) = 33.33 cu ft.
- Add the extraMultiply by 1 plus the waste allowance: 33.33 × 1.10 = 36.67 cu ft, which is 1.36 cubic yards (÷ 27).
- Divide by the bag yieldAn 80 lb bag of QUIKRETE Concrete Mix makes about 0.60 cu ft: 36.67 ÷ 0.60 = 61.1, so you buy 62 bags.
| QUIKRETE Concrete Mix bag | Yield per bag | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 cu ft | 90 |
| 50 lb | 0.375 cu ft | 72 |
| 60 lb | 0.45 cu ft | 60 |
| 80 lb | 0.60 cu ft | 45 |
| 90 lb | 0.675 cu ft | 40 |
Yields: QUIKRETE Concrete Mix No. 1101 data sheet (revised October 2022, yields stated as approximate). Waste allowance: Sakrete, Estimating Bagged Concrete Jobs. 27 cu ft = 1 cu yd: NIST Handbook 44, Appendix C. Bags per yard in more detail: how many bags of concrete in a yard.
Bags for common slabs
4 inches thick unless noted, with 10% extra, using the QUIKRETE yields above.
| Slab | Cubic feet with 10% | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 4 × 4 ft | 5.87 | 0.22 | 10 | 14 |
| 10 × 10 ft | 36.67 | 1.36 | 62 | 82 |
| 10 × 12 ft | 44 | 1.63 | 74 | 98 |
| 12 × 12 ft | 52.8 | 1.96 | 88 | 118 |
| 10 × 20 ft | 73.33 | 2.72 | 123 | 163 |
| 10 × 10 ft, 6 in thick | 55 | 2.04 | 92 | 123 |
Questions people ask
- How many 80 lb bags of concrete make a yard?
- 45. A cubic yard is 27 cu ft, and QUIKRETE lists about 0.60 cu ft per 80 lb bag of Concrete Mix, so 27 ÷ 0.60 = 45 bags before any extra.
- How many bags for a 10 × 10 slab?
- At 4 inches thick, 56 bags of 80 lb mix fill it exactly (33.33 ÷ 0.60 = 55.6). With 10% extra for spills and uneven ground, buy 62.
- How thick should a slab be?
- That depends on what it carries and on your local building code, so check with your building department for anything structural. QUIKRETE says its Concrete Mix is meant for pours 2 inches thick or more.
- Does a different brand change the count?
- It can. Yields depend on the mix, so check the label on the bag and compare its cubic feet with the figures here. The math is the same: cubic feet needed ÷ cubic feet per bag.
- When should I order ready-mix instead?
- When the bag count gets large, compare the cost and labor of mixing by hand with a quote for delivered concrete. Ready-mix is sold by the cubic yard, which the list shows next to the bags.