How Many Bags of Concrete Do I Need?
One 80lb bag = 0.6 cubic feet. 45 bags = 1 cubic yard. Use a calculator.
How Many Bags of Concrete Do I Need? Complete Guide
For small projects, bagged concrete is more practical than ordering a truck. But figuring out how many bags you need can be confusing. This guide shows you exactly how to calculate the number of bags needed for any project.
Bag Coverage Basics
80-pound bag: Covers approximately 0.6 cubic feet when mixed
60-pound bag: Covers approximately 0.45 cubic feet when mixed
40-pound bag: Covers approximately 0.3 cubic feet when mixed
Key conversion: 1 cubic yard = 27 cubic feet = approximately 45 bags (80 lb) = approximately 60 bags (60 lb) = approximately 90 bags (40 lb)
The Calculation Formula
Step 1: Calculate cubic feet needed (Length × Width × Depth in feet)
Step 2: Divide by bag coverage (0.6 for 80 lb, 0.45 for 60 lb, 0.3 for 40 lb)
Step 3: Round up and add 10% for waste
Real-World Examples
Example 1: Small Patio (10x10 feet, 4 inches thick)
Calculation: 10 × 10 × 0.33 = 33 cubic feet
80 lb bags: 33 ÷ 0.6 = 55 bags
With waste: 55 × 1.1 = approximately 61 bags
Order: 60-65 bags
Example 2: Sidewalk (3x20 feet, 4 inches thick)
Calculation: 3 × 20 × 0.33 = 19.8 cubic feet
80 lb bags: 19.8 ÷ 0.6 = 33 bags
With waste: 33 × 1.1 = approximately 36-37 bags
Order: 40 bags
Example 3: Post Holes (6 holes, 12 inches diameter, 36 inches deep)
Volume per hole: π × (0.5)² × 3 = 2.36 cubic feet
Total: 2.36 × 6 = 14.16 cubic feet
80 lb bags: 14.16 ÷ 0.6 = approximately 24 bags
With waste: 24 × 1.1 = approximately 26-27 bags
Order: 30 bags
When to Use Bags vs. Truck
Use bags if:
- Project is less than 1 cubic yard
- You have time to mix multiple bags
- Access is difficult for trucks
- You want to work at your own pace
Order a truck if:
- Project is more than 1 cubic yard
- You need it done quickly
- You want consistent mix quality
- Cost efficiency matters (trucks are cheaper per yard)
Mixing Considerations
Mixing 50+ bags is extremely labor-intensive. Consider:
- Renting a mixer for large projects
- Having help (mixing is hard work)
- Time required (each bag takes 5-10 minutes to mix properly)
The Bottom Line
Calculate your cubic feet needed, divide by bag coverage (0.6 for 80 lb bags), add 10% for waste, and round up. For projects over 1 cubic yard, consider ordering a truck instead—it's typically more cost-effective and less labor-intensive.
Need help calculating your concrete needs? Contact Local Concrete Contractor. We can help you determine whether bags or a truck delivery makes more sense for your project.
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