Concrete Calculator

The Concrete Calculator estimates the volume of concrete for a rectangular pour and converts it to cubic feet, cubic yards, and whole bags. Enter length, width, depth, and the bag coverage assumption.

Formula

Depth is entered in inches and converted to feet:

$\text{Cubic feet}=\text{Length}\times\text{Width}\times\frac{\text{Depth in inches}}{12}$ $\text{Cubic yards}=\frac{\text{Cubic feet}}{27}$ $\text{Bags}=\operatorname{ceil}(\text{Cubic yards}\times\text{Bags per cubic yard})$

The default coverage is 45 bags per cubic yard, but bag yield varies by product.

Worked example

For a 12 ft by 10 ft slab that is 4 inches deep:

1. Volume: 12 x 10 x (4 / 12) = 40 cubic feet.
2. Cubic yards: 40 / 27 = 1.48 cubic yards.
3. At 45 bags per cubic yard: ceil(1.48 x 45) = 67 bags.

Questions

Why is depth entered in inches?

Common slab depths are specified in inches. The calculator converts that value to feet before multiplying the dimensions.

Why does the bag result round up?

Concrete bags are whole units and a fractional result would under-order the pour, so the calculator uses a ceiling operation.

Does the result include waste?

No explicit waste factor is added. Use a conservative bag-yield input and consider a separate allowance for uneven excavation, spillage, and over-excavation.

Limitations

The model covers one rectangular volume. It does not calculate footings, steps, cylinders, reinforcement, delivery minimums, or product-specific yield beyond the bag-coverage value you enter. Confirm quantities with the supplier or contractor.