Concrete Bag Coverage Calculator
An 80 lb bag of concrete covers about 1.8 square feet at 4 inches thick. A 60 lb bag covers about 1.35 square feet, and a 40 lb bag covers about 0.9 square feet.
Your result
- Coverage: — sq ft
Quick answer
An 80 lb bag of concrete covers about 1.8 square feet at 4 inches thick. A 60 lb bag covers about 1.35 square feet, and a 40 lb bag covers about 0.9 square feet.
How the calculator works
Coverage = bag yield in cubic feet ÷ (thickness in feet). Example: 0.60 cu ft ÷ (4 ÷ 12) = 1.8 sq ft.
What “bag yield” really means
Concrete bags are labeled by dry weight, not by finished volume. The number that matters for coverage is yield: the cubic feet of mixed concrete the bag produces after water is added.
An 80 lb bag yields about 0.60 cubic feet, a 60 lb bag about 0.45, a 50 lb bag about 0.375, and a 40 lb bag about 0.30. These are manufacturer figures for standard preblended mix, not estimates.
If you switch bag sizes, recalculate rather than guessing. A 60 lb bag is not “a little less” than an 80 lb bag — it is 25% less concrete by volume.
How to use this calculator
Enter the bag size you plan to buy and the finished pour thickness. The result is the square feet one bag will cover at that depth.
If you already know your slab area, divide that area by the coverage number to get the number of bags before waste. Then add 10% for normal jobs or 15% for uneven ground.
When to buy more than the calculator says
Buy extra if your forms are uneven, the subgrade is soft, or you are mixing by hand for the first time.
For small pours, one spare bag is cheap insurance. For larger slabs, order by the cubic yard instead of carrying dozens of bags.
Note. Coverage is for mixed concrete, not dry mix. A bag that yields 0.60 cubic feet of concrete does not cover 0.60 cubic feet of dry volume after water is added.
| Bag size | 2" | 3" | 4" | 6" |
|---|---|---|---|---|
| 80 lb | 3.60 | 2.40 | 1.80 | 1.20 |
| 60 lb | 2.70 | 1.80 | 1.35 | 0.90 |
| 50 lb | 2.25 | 1.50 | 1.13 | 0.75 |
| 40 lb | 1.80 | 1.20 | 0.90 | 0.60 |
FAQ
How many square feet does an 80 lb bag of concrete cover?
About 1.8 square feet at 4 inches thick, 2.4 square feet at 3 inches, and 3.6 square feet at 2 inches.
How many 80 lb bags do I need for 100 square feet at 4 inches?
About 56 bags, or 62 with a 10% waste margin.
Does a 60 lb bag cover less than an 80 lb bag?
Yes. A 60 lb bag yields about 0.45 cubic feet, so it covers about 25% less area than an 80 lb bag at the same thickness.
Why does thickness matter more than bag weight?
Because coverage is volume divided by depth. A thin pour spreads the same bag over more square feet, but a thick pour uses it up faster.
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Last updated: 2026-10-29