Concrete
Concrete Bags Calculator: How Many Bags Do You Need?
Understand concrete bag yields, convert volume into bags, and compare 40, 60 and 80 lb bags (and 20–30 kg bags) with worked examples and a quick reference table.
2 min read
- Dual US / Metric
- +10% Waste Allowance
- Free · Runs in Your Browser
Concrete Bag Calculator
Pre-mixed concrete bags are convenient for small pours, but their yield is often misunderstood. Enter your project dimensions, or a volume you already know, and compare how many bags of each common size you would need.
Enter your measurements
Enter your measurements and press Calculate to see quantities, a material breakdown and an optional cost estimate.
How the calculation works
- Bags = (Volume × (1 + Waste %)) ÷ Yield per bag
- Round up to the next whole bag
The yield is the volume of hardened concrete one bag makes once mixed with water. It is printed on the bag and depends on the product, so the weight of the bag alone is not enough.
Assumptions used
- Typical yields: 40 lb ≈ 0.30 ft³, 60 lb ≈ 0.45 ft³, 80 lb ≈ 0.60 ft³, 20 kg ≈ 9.4 L, 25 kg ≈ 11.7 L, 30 kg ≈ 14 L.
- Metric bag yields are approximate and vary more between brands; use the custom yield where possible.
Example calculation
You need 0.5 cubic yards of concrete and want to compare bag sizes (no waste added).
- 10.5 yd³ × 27 = 13.5 ft³
- 280 lb bags: 13.5 ÷ 0.60 = 22.5 → 23 bags
- 360 lb bags: 13.5 ÷ 0.45 = 30 bags
- 440 lb bags: 13.5 ÷ 0.30 = 45 bags
Result: 23 × 80 lb bags weigh about 1,840 lb in total, so plan transport accordingly.
How to measure your project
- If you already have a volume from another calculator, choose "Required concrete volume" and enter it directly.
- Check the yield on the bag you intend to buy. Fast-setting and high-strength mixes can have different yields.
Frequently asked questions
How much does an 80 lb bag of concrete cover?
An 80 lb bag typically yields about 0.60 ft³. At 4 inches thick that covers roughly 1.8 ft²; at 2 inches thick about 3.6 ft².
Are bigger bags better value?
Larger bags usually cost less per cubic foot, but they are heavy to lift and mix. Smaller bags can be easier for one person and for filling post holes one at a time.
How much water does a bag of concrete need?
Follow the manufacturer's instructions. As a rough guide, an 80 lb bag often needs about 3 quarts (around 3 litres) of water, but adding too much weakens the concrete.
Related guides
ConcreteHow Much Concrete Do I Need for a Concrete Slab?
Learn how to calculate concrete for a slab step by step, convert to cubic yards or cubic metres, add the right waste allowance and decide between bags and ready-mix.
3 min read
Results are estimates based on the measurements and assumptions you enter. Always confirm product specifications, local building codes and final quantities with your supplier or a qualified professional. See our disclaimer.