Construction Calculators
Concrete Calculator
Calculate concrete volume needed for slabs, footings, and columns. Get cubic yards, cubic feet, and the number of 40 / 60 / 80 lb bags required.
Inputs
Concrete needed
Fill the form and press Calculate.
10x10 concrete slab calculator: worked example
A 10 ft x 10 ft slab poured 4 in thick holds 10 x 10 x (4 / 12) = 33.33 cubic feet of concrete. Divide by 27 for cubic yards: 1.23 cu yd. Multiply by 0.0283168 for cubic metres: 0.94 m³. With a 10% waste allowance that becomes 36.7 cu ft, 1.36 cu yd or 1.04 m³.
For bagged mix, divide the cubic feet by the bag yield and round up. A 10x10x4 in slab with 10% waste needs about 123 bags of 40 lb, 82 bags of 60 lb, or 62 bags of 80 lb mix (112 / 75 / 56 with no waste allowance).
Common slab sizes, all with 10% waste in the last two columns. Press a size to load it into the calculator above.
| Slab (L x W, thickness) | Exact volume (cu yd / m³) | With 10% waste (cu yd / m³) | Bags with 10% waste (40 / 60 / 80 lb) |
|---|---|---|---|
| 1.23 / 0.94 | 1.36 / 1.04 | 123 / 82 / 62 | |
| 1.85 / 1.42 | 2.04 / 1.56 | 184 / 123 / 92 | |
| 1.48 / 1.13 | 1.63 / 1.25 | 147 / 98 / 74 | |
| 1.78 / 1.36 | 1.96 / 1.50 | 176 / 118 / 88 | |
| 2.47 / 1.89 | 2.72 / 2.08 | 245 / 163 / 123 |
Bag yields are the manufacturer's approximate figures: 0.30, 0.45 and 0.60 cu ft for 40, 60 and 80 lb bags (QUIKRETE Concrete Mix data sheet). Other brands differ, so check the bag. Unit conversion: 1 cu ft = 0.02831685 m³ (NIST SP 811, Appendix B.8). This is a volume estimate, not a structural design; sub-base, reinforcement and thickness depend on your local code and soil.
Concrete slab questions
How much concrete do I need for a 10x10 slab, 4 inches thick?
1.23 cubic yards (0.94 cubic metres) exactly, or about 1.36 cubic yards (1.04 m³) with a 10% waste allowance.
How many 80 lb bags of concrete make a 10x10 slab?
At 0.60 cu ft per 80 lb bag, a 10x10x4 in slab needs 56 bags exactly or 62 with 10% waste. Using 60 lb bags (0.45 cu ft) it is 82, and with 40 lb bags (0.30 cu ft) it is 123.
How do I convert cubic feet of concrete to cubic yards?
Divide by 27, since a cubic yard is 3 x 3 x 3 feet. Multiply cubic feet by 0.02831685 to get cubic metres.
How much waste allowance should I add?
The calculator defaults to 10% to cover uneven sub-grade, spillage and slightly over-thick edges. Set it to 0 to see the exact geometric volume.