How much does an 80 lb bag of concrete cover?
One 80 lb bag of concrete mix yields about 0.60 cubic feet, which covers roughly 1.8 square feet at a standard 4 inch slab thickness, or 1.2 square feet at a 6 inch thickness. A 60 lb bag covers about three quarters of that, and a 40 lb bag about half, since coverage scales directly with the bag's yield.
Use the chart below to find the right coverage rate for your thickness, then divide your area by it.
Coverage chart by thickness
Square feet of coverage from one bag, at each common pour thickness. Figures use the published QUIKRETE Concrete Mix yields of 0.30 cubic feet (40 lb), 0.45 cubic feet (60 lb), and 0.60 cubic feet (80 lb) per bag.
| Thickness | 40 lb bag | 60 lb bag | 80 lb bag |
|---|---|---|---|
| 2 in | 1.8 sq ft | 2.7 sq ft | 3.6 sq ft |
| 3 in | 1.2 sq ft | 1.8 sq ft | 2.4 sq ft |
| 4 in (standard slab) | 0.9 sq ft | 1.35 sq ft | 1.8 sq ft |
| 5 in | 0.72 sq ft | 1.08 sq ft | 1.44 sq ft |
| 6 in | 0.6 sq ft | 0.9 sq ft | 1.2 sq ft |
| 8 in | 0.45 sq ft | 0.675 sq ft | 0.9 sq ft |
These are planning figures based on the manufacturer's published yield, not an actual poured measurement. Always check your bag's label, since yield can vary slightly by product line.
Turning coverage into bags
Work out the area you are pouring in square feet, multiply by the thickness in feet to get cubic feet, add a waste factor, then divide by the bag yield and round up, since bags are sold whole.
Example: you need to cover 10 square feet at a 4 inch thickness with 80 lb bags.
| Thickness in feet | 4 ÷ 12 = 0.333 ft |
| Volume | 10 × 0.333 = 3.33 cu ft |
| No waste factor | 3.33 ÷ 0.60 = 5.56, round up to 6 bags |
| Plus 10 percent waste | 3.33 × 1.10 = 3.67 cu ft |
| With waste factor | 3.67 ÷ 0.60 = 6.11, round up to 7 bags |
That one waste factor is the difference between 6 bags and 7. It is cheap insurance against running short mid-pour. Run your own area, thickness, and waste factor in the concrete calculator.
What changes real-world coverage
- Sub-grade unevenness. A form or excavation that is not a uniform depth uses more material in the low spots, so the bag yield figure, which assumes a perfectly even thickness, understates what you actually need.
- Over-excavation. Digging a footing or base slightly deeper than planned, intentionally or not, eats directly into your coverage.
- Mixing water. Adding more water than the bag's instructions call for increases workability but reduces strength and can slightly change the set volume; always follow the water ratio on the bag.
- Bag size choice. Smaller bags are easier to carry and mix in small batches by hand, but need more bags and more mixing cycles for the same job as larger bags.
Frequently asked questions
How much does an 80 lb bag of concrete cover?
An 80 lb bag of concrete mix yields about 0.60 cubic feet, which covers about 1.8 square feet at a 4 inch thickness or 1.2 square feet at a 6 inch thickness. Coverage drops as thickness increases, since the same volume spreads over a smaller area.
How much does a 60 lb bag of concrete cover?
A 60 lb bag yields about 0.45 cubic feet, covering about 1.35 square feet at 4 inches thick or 0.9 square feet at 6 inches thick, three quarters of what an 80 lb bag covers at the same thickness.
How much does a 40 lb bag of concrete cover?
A 40 lb bag yields about 0.30 cubic feet, covering about 0.9 square feet at 4 inches thick or 0.6 square feet at 6 inches thick, half of what an 80 lb bag covers at the same thickness.
How many 80 lb bags do I need per square foot?
At a standard 4 inch slab thickness, one 80 lb bag covers 1.8 square feet, so divide your area in square feet by 1.8 and round up. For 10 square feet that is 5.6, rounded up to 6 bags before any waste factor is added.
Does coverage change with a thicker pour?
Yes, coverage area is inversely proportional to thickness. Doubling the thickness from 4 inches to 8 inches halves the square footage a single bag covers, from 1.8 square feet down to 0.9 square feet for an 80 lb bag.
Should I add a waste factor to bag coverage math?
Yes. A 10 percent waste factor is standard for a level, well-compacted pour, and it is cheaper to have an extra bag on hand than to stop mid-pour. Adding 10 percent waste to a 10 square foot, 4 inch thick pour changes the 80 lb bag count from 6 to 7.