Concrete Calculator
Calculate concrete yardage from your form dimensions, then estimate bags or a quoted material cost.
Free calculator. Mixed units and fractions welcome.1 yd³ = 27 ft³
At a glance
Concrete Calculator
Concrete volume in cubic yards equals length in feet × width in feet × thickness in inches ÷ 324. For other shapes, calculate the footprint area before applying thickness.
Materials
How to calculate concrete yardage
Measure inside the forms. For a rectangular slab, use its finished length, width, and thickness. The calculator accepts feet and inches together, independent metric units, round forms, and several sections with different depths. If you already know the slab area, use square feet and thickness to find the volume.
Cubic yards = length (ft) × width (ft) × thickness (in) ÷ 324
A 12 ft by 10 ft slab at 4 inches thick contains 40 cubic feet, or about 1.481 cubic yards. This is its measured geometric volume. An allowance or a supplier’s order increment is a separate choice.
For a slab with a thickened edge, calculate the ordinary slab first, then add only the extra edge volume below that thickness. This avoids counting the same concrete twice.
Materials
Concrete bags: use the finished yield
A bag’s weight is not its finished concrete volume. Divide the required cubic feet by the mixed yield printed on the specific bag, then round up to a whole bag. Optional ordering adjustments are applied before the bag count.
| Specific product example | Approximate mixed yield | Whole bags for 1 yd³ |
|---|---|---|
| QUIKRETE Concrete Mix, 60 lb | 0.45 ft³ | 60 |
| QUIKRETE Concrete Mix, 80 lb | 0.60 ft³ | 45 |
These yields belong to the cited QUIKRETE product. Other products and bag sizes can differ. For the 40 ft³ slab above, a stated 0.60 ft³ yield requires 67 whole bags before any extra allowance.
Materials
Concrete cost and ordering
Enter your supplier’s price per cubic yard, cubic foot, or cubic meter under Ordering options. The result separates measured volume, an optional allowance, and the planned quantity. Material cost uses the planned quantity.
- Ask about minimum orders, delivery, short load charges, and tax. These are not automatically included.
- Use the actual specified slab thickness and mix. This calculator does not choose structural thickness, reinforcement, or concrete strength.
- For bagged mixes, compare finished yield and the number of bags. For a ready mix order, confirm the supplier’s selling increment.
Common questions
Concrete questions, answered.
Is a cement calculator the same as a concrete calculator?
People sometimes use cement to mean concrete, but cement is one ingredient of concrete. This tool estimates finished concrete volume. It does not calculate the cement, aggregate, and water proportions of a mix.
Can I calculate a round footing or post hole?
Yes. Choose Circle and enter its diameter or radius and its depth. The model is a straight cylinder. A tapered hole or an irregular footing needs separate measured sections or a project specific model.
How much concrete do I need for several slabs?
Use Add another area for each section. Give every section its own dimensions and thickness. The calculator adds the unrounded volumes before applying any ordering allowance.
Does one cubic yard always need 45 bags?
Only when each bag has a finished yield of 0.60 cubic feet, and no additional material is needed. One cubic yard is 27 cubic feet, so 27 ÷ 0.60 = 45. Use your product’s actual yield.
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