Calculate exactly how many bags of concrete you need for slabs, footings, posts, and repairs. Get instant estimates for 40lb, 60lb, or 80lb bags with cost breakdowns.
Recommended: 10% for spillage and uneven subgrade
Ready to calculate
Enter your project dimensions
Easier to carry
Yield: 0.3 cu ft
At 4": 0.9 sq ft
Price: $4.5
Most common
Yield: 0.45 cu ft
At 4": 1.4 sq ft
Price: $5.5
Best value
Yield: 0.6 cu ft
At 4": 1.8 sq ft
Price: $6.5
Why expert review matters
Every calculator is reviewed by certified professionals to ensure accuracy.Hawkin's CCP, CEP certification ensures professional-grade precision.
| Project Size | 2" Deep | 4" Deep | 6" Deep |
|---|---|---|---|
| 2' × 2' | 2 | 3 | 5 |
| 4' × 4' | 5 | 9 | 14 |
| 6' × 6' | 10 | 20 | 30 |
| 8' × 8' | 18 | 36 | 54 |
| 10' × 10' | 28 | 56 | 84 |
How many bags of concrete do I need?
Calculate cubic feet (L × W × depth), then divide by 0.60 for 80lb bags, 0.45 for 60lb, or 0.30 for 40lb bags.
What does an 80lb bag cover?
One 80lb bag yields 0.60 cu ft, covering about 1.8 sq ft at 4" thick or 3.6 sq ft at 2" thick.
How thick should concrete be?
4" for patios/sidewalks, 6" for driveways, 8-12" for footings and heavy loads.
Bags vs ready-mix concrete?
Use bags for under 1 cubic yard. For larger projects, ready-mix ($125-150/yd) saves time and labor.
The calculator determines total concrete volume needed by multiplying length × width × depth (converted to feet). It then divides by the yield of your selected bag size to determine how many bags you need. We include your specified overage percentage to account for spillage, uneven ground, and mixing losses that occur on every job.
Formula
Volume (cu ft) = Length × Width × (Depth ÷ 12)
Bags Needed = Volume ÷ Bag Yield × (1 + Waste %)