Bags of Concrete Calculator
Enter dimensions to calculate bags needed.
Bags of Concrete Formula
Understanding Concrete Bags
Concrete Bag Sizes and Coverage
| Bag Size | Cubic Feet per Bag | Bags per Cubic Yard | Water Required |
|---|---|---|---|
| 40 lb bag | 0.30 cu ft | 90 bags | 3 quarts |
| 50 lb bag | 0.375 cu ft | 72 bags | 3.75 quarts |
| 60 lb bag | 0.45 cu ft | 60 bags | 1/2 gallon |
| 80 lb bag | 0.60 cu ft | 45 bags | 3/4 gallon |
The 80-lb bag offers the best value per cubic foot. The 60-lb bag is the practical choice for most DIYers.
When to Use Bags vs. Ready-Mix
- Bags (under 1 CY): Fence posts, small footings, patching. Cost: - per bag (- per CY).
- Ready-mix truck (1+ CY): Driveways, patios, foundations. Cost: - per CY.
The crossover point is approximately 0.75-1 cubic yard. Above that, ready-mix is cheaper, faster, and more consistent.
Mixing Concrete from Bags
Mix in a wheelbarrow or portable mixer. Add water gradually. The correct consistency is like thick oatmeal. One person can reasonably mix 10-15 bags (80 lb) per hour with a wheelbarrow.
Bags of Concrete Calculator FAQ
Calculate volume in cubic feet (length x width x depth in feet), then divide by cubic feet per bag: 0.30 for 40-lb, 0.45 for 60-lb, or 0.60 for 80-lb bags. Add 10% for waste.
You need 45 bags of 80-lb concrete mix per cubic yard. Each bag yields 0.60 cubic feet, and there are 27 cubic feet per cubic yard.
A standard 4x4 post in a 10-inch diameter, 36-inch deep hole requires 2-3 bags of 80-lb concrete. A 6x6 post needs 4-5 bags.
Ready-mix is cheaper above 0.75-1 cubic yard. Bags cost - per CY. Ready-mix costs - per CY delivered. Below 1 CY, bags avoid short-load surcharges.
Add approximately 3/4 gallon (3 quarts) of water per 80-lb bag. Start with slightly less and add gradually until reaching a thick, workable consistency.
Standard mix sets in 24-48 hours and reaches full strength in 28 days. Fast-setting concrete sets in 20-40 minutes and reaches walking strength in 2 hours.