Concrete bag calculator
How many bags of concrete do you need?
Enter your slab's dimensions to get bag counts for 40, 60 and 80 lb bags side by side, so you can pick the size that fits your budget and how much you want to carry.
Enter your dimensions
National average is $150–$200 per cubic yard, delivered — edit it to match your local supplier.
Results
Bagged mix alternative
- 40 lb bags—
- 60 lb bags—
- 80 lb bags—
Bag counts include your waste % and round up to whole bags.
- Volume needed
- —
- Recommended order
- —
- Estimated cost
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Estimates only — bag yield varies slightly by brand; check the yield printed on your specific bag.
How it's calculated
Volume ÷ yield per bag, rounded up.
Each bag size yields a fixed amount of cured concrete: roughly 0.3 ft³ for a 40 lb bag, 0.45 ft³ for a 60 lb bag, and 0.6 ft³ for an 80 lb bag. We calculate your slab's total volume (including waste), divide by the yield for each bag size, and round up — since you can't buy part of a bag.
Quick reference
Bags for common slab sizes.
At 4 inches thick. Pricing a bigger pour? Seehow many bags make a yard — and the point where a ready-mix truck gets cheaper. Setting posts instead? Seebags per fence post.
| Slab (4″ thick) | Cubic yards | Order (+10%) | 60 lb bags | 80 lb bags |
|---|---|---|---|---|
| 4 × 4 ft | 0.20 yd³ | 0.22 yd³ | 14 | 10 |
| 8 × 8 ft | 0.79 yd³ | 0.87 yd³ | 53 | 40 |
| 10 × 10 ft | 1.23 yd³ | 1.36 yd³ | 82 | 62 |
| 10 × 12 ft | 1.48 yd³ | 1.63 yd³ | 98 | 74 |
| 12 × 12 ft | 1.78 yd³ | 1.96 yd³ | 118 | 88 |
| 10 × 20 ft | 2.47 yd³ | 2.72 yd³ | 163 | 123 |
| 12 × 20 ft | 2.96 yd³ | 3.26 yd³ | 196 | 147 |
| 16 × 16 ft | 3.16 yd³ | 3.48 yd³ | 209 | 157 |
| 20 × 20 ft | 4.94 yd³ | 5.43 yd³ | 326 | 245 |
| 24 × 24 ft | 7.11 yd³ | 7.82 yd³ | 470 | 352 |
Bag counts include 10% waste and round up to whole bags.
FAQ
Common questions
How much area does one bag of concrete cover?
At 4 inches thick, a 40 lb bag covers about 0.9 sq ft, a 60 lb bag about 1.35 sq ft, and an 80 lb bag about 1.8 sq ft. Thinner or thicker pours change the coverage proportionally — the calculator does this math for your exact dimensions.
40, 60 or 80 lb bags — which should I buy?
80 lb bags are the most cost-efficient per cubic foot and standard for slabs and footings. 60 lb bags are a common middle ground. 40 lb bags cost more per cubic foot but are easier to carry and mix by hand — a reasonable trade for small repairs or if you're working alone.
Do bag counts already include extra for waste?
Yes. The bag counts above are based on your recommended order (volume plus your waste percentage), then rounded up to the next whole bag, since suppliers don't sell partial bags.
Is bagged concrete cheaper than ready-mix delivery?
Per cubic yard, bagged concrete usually costs more than ready-mix delivered by truck — but ready-mix has delivery minimums (often 1 yard or more) and short discharge windows. For small pours, bags are usually still the practical choice despite the higher per-yard cost.
Building something specific?