Concrete calculator
Enter the slab's length, width and thickness. Add a little extra for uneven ground and spillage.
Your estimateEstimate
- Volume with extra
- 36.7 ft³
- 80 lb bags (0.60 ft³ each)
- 62
- 60 lb bags (0.45 ft³ each)
- 82
- 40 lb bags (0.30 ft³ each)
- 123
Concrete needed1.36 yd³
How it is calculated
Volume = length × width × thickness, plus the extra percentage. One cubic yard is 27 cubic feet.
Premixed bags yield about 0.60 ft³ (80 lb), 0.45 ft³ (60 lb) and 0.30 ft³ (40 lb). Check the bag, because yields vary by brand.
Worked example
With the starting values shown in the form, the result is 1.36 yd³ (concrete needed). Change any number and the estimate updates as you type.
Tips
- Above roughly one cubic yard, ready-mix delivery is often cheaper and faster than mixing bags.
- Measure thickness in several spots; a 4 in slab that ends up 4.5 in thick needs 12.5% more concrete.
Questions
- How many 80 lb bags make a cubic yard?
- About 45. A cubic yard is 27 ft³ and each 80 lb bag yields about 0.60 ft³.
- How much concrete for a 10 × 10 slab, 4 inches thick?
- 33.3 ft³, or 1.23 cubic yards, before extra. With 10% extra that is about 1.36 yd³ or 62 bags of 80 lb.
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