Concrete Bag Calculator
Find out how many 40 lb, 50 lb, 60 lb or 80 lb bags of concrete you need for your project.
This concrete bag calculator converts your project's length, width and pour depth into total volume and translates that into the exact number of bags to buy, based on your chosen bag size. It works for slabs, footings, posts and small pours where bagged concrete is more practical than a ready-mix delivery. Enter your dimensions, pick a bag size, and add a waste percentage to see how many bags to order and the estimated total weight.
Your Estimate
Total Area
100.0 ft²
Total Concrete Volume
1.23 yd³
Cubic Feet
33.33 ft³
Cubic Yards
1.23 yd³
Bags Required
56 bags
Bags Including Waste
62 bags
Estimated Total Weight
4,960 lbs
Based on a published yield of approximately 0.600 cubic feet per 80 lb bag. Bag counts are rounded up to the nearest full bag. Actual yield can vary slightly by brand.
Results Actions
Estimates are approximate. Confirm bag yield on your product's packaging before purchasing.
Common Thickness Reference Table
How to Use the Concrete Bag Calculator
- 1Measure the length and width of your slab, footing or post hole area.
- 2Measure your pour depth — 4 inches is standard for slabs, deeper for footings.
- 3Select the bag size you plan to buy: 40 lb, 50 lb, 60 lb or 80 lb.
- 4Choose a waste percentage — 10% covers most straightforward pours.
- 5Read your results instantly: total volume, cubic feet, cubic yards, bags needed and total weight.
Example Calculation
Say you're pouring a 10 ft x 10 ft slab at 4 inches deep using 80 lb bags with a 10% waste factor. Total area = 10 × 10 = 100 sq ft. Depth in feet = 4 ÷ 12 = 0.333 ft. Volume = 100 × 0.333 = 33.3 ft³ (about 1.23 yd³). An 80 lb bag yields about 0.60 ft³, so bags required = 33.3 ÷ 0.60 ≈ 56 bags. With 10% waste, volume becomes 36.7 ft³, which rounds up to 62 bags — weighing an estimated 4,960 lbs in total.
Accuracy & Assumptions
- Results are estimates only and are meant for planning purposes.
- Bag yields can vary slightly by manufacturer — check the exact yield printed on your bag.
- Consider ordering an additional 5–10% extra bags for spillage and uneven subgrade.
- Verify all slab, footing or post hole measurements before purchasing bagged concrete.
- Check local building codes and consult a professional for structural or load-bearing pours.
Frequently Asked Questions
How many 80 lb bags of concrete do I need per cubic yard?
An 80 lb bag yields about 0.60 cubic feet of mixed concrete, so it takes roughly 45 bags to make one cubic yard (27 cubic feet ÷ 0.60 ft³ ≈ 45 bags).
What is the difference between 40 lb, 50 lb, 60 lb and 80 lb bags?
The number refers to the dry weight of the bag. Heavier bags yield more mixed concrete per bag (roughly 0.0075 cubic feet per pound), so fewer 80 lb bags are needed than 40 lb bags for the same job, though 80 lb bags are much heavier to carry and mix.
How much waste should I add for bagged concrete?
Most DIYers add 10% extra to cover spillage, uneven subgrade and mixing loss. Add 15% or more for small or irregularly shaped pours where waste is harder to control.
Can I use this calculator for footings and posts, not just slabs?
Yes. Enter the length and width of the footing or the diameter converted to a square/rectangular equivalent, along with the pour depth, and the calculator will estimate bag counts the same way.
Is bagged concrete cheaper than ready-mix delivery?
For small jobs (under 1 cubic yard) bagged concrete is usually more convenient and cost-effective. For larger pours, ready-mix delivery is typically cheaper per cubic yard and saves significant labor.
This calculator provides an estimate for planning purposes only. Bag yield, mix design and manufacturer specifications vary — always confirm the exact yield printed on your bag before purchasing.