Premix Concrete Calculator
Multiply length by width by depth (converted to feet) to get cubic feet, then divide by your bag’s yield — a standard 80 lb bag yields about 0.60 cubic feet of mixed concrete.
Quick Answer
Multiply length by width by depth (converted to feet) to get cubic feet, then divide by your bag’s yield — a standard 80 lb bag yields about 0.60 cubic feet of mixed concrete.
Premix Concrete Calculator
Enter your values below for an instant result, then see the formula, worked example, and common mistakes.
Enter your values and click calculate.
How to Use This Calculator
Measure length and width in feet for the slab, footing, or post hole you are filling.
Enter the thickness of the pour in inches — 4 inches is standard for walkways and patios, thicker for driveways.
Premix bags commonly come in 40 lb, 60 lb, and 80 lb sizes with different cubic-foot yields once mixed with water.
Always round up to the next full bag, and add 1-2 extra bags to cover spillage, uneven subgrade, and small measurement errors.
Formula
Cubic feet = Length x Width x (Depth in inches / 12). Bags needed = Cubic feet / bag yield (cubic feet per bag).
Reference Table: Premix Concrete Bag Yields
| Bag size | Mixed yield | Bags per cubic yard |
|---|---|---|
| 40 lb | ~0.30 cu ft | ~90 bags |
| 60 lb | ~0.45 cu ft | ~60 bags |
| 80 lb | ~0.60 cu ft | ~45 bags |
Common Mistakes to Avoid
- Using the bag weight (40/60/80 lb) as if it were the yield in cubic feet — yield is a separate, smaller number specific to each bag size.
- Forgetting to convert pour depth from inches to feet before multiplying (a common source of 12x errors).
- Not rounding up to full bags, or not adding a small overage for spillage and uneven subgrade.
- Using bagged premix for large pours (over roughly 1 cubic yard) where a ready-mix truck delivery is usually far more cost-effective per cubic yard.
When the Estimate May Be Wrong
For pours larger than about 1 cubic yard (which would need 45+ bags of 80 lb mix), ready-mix delivery from a concrete supplier is usually cheaper and more consistent than bagged premix. Bag yield can also vary slightly by brand and water ratio — check the bag’s label for the manufacturer’s stated yield.
FAQs
How many 80 lb bags of concrete make a cubic yard?
About 45 bags, since each 80 lb bag yields roughly 0.60 cubic feet and a cubic yard is 27 cubic feet.
How much concrete does an 80 lb bag make?
An 80 lb bag of premix concrete yields about 0.60 cubic feet once mixed with water.
Is it cheaper to use bags or a concrete truck?
For pours over about 1 cubic yard, ready-mix truck delivery is usually more cost-effective than buying dozens of bags.
Sources and Methodology
Bag yield figures (0.60 cu ft per 80 lb bag, 0.45 cu ft per 60 lb bag, 0.30 cu ft per 40 lb bag) reflect published manufacturer specifications from major premix concrete brands (e.g. Quikrete, Sakrete), current as of 2026.
