Concrete Calculator

Use this concrete calculator to estimate material volume for simple slabs and small pours. It converts length, width, and depth into cubic feet, cubic yards, and premix bag counts.

Formula

For a rectangular slab:

$V = L \times W \times D$

Depth is entered in inches and converted to feet before multiplication. Waste is then added to cover uneven bases, spillage, and ordering tolerance.

Premix bag estimates

The calculator uses common approximate yields:

Actual yield can vary by product and water content, so check the bag label before ordering.

Example

A 10 ft by 10 ft slab at 4 inches deep:

$10 \times 10 \times \frac{4}{12}=33.33\text{ cu ft}$

With 10% waste, the estimate becomes about 36.67 cu ft, or 1.36 cubic yards.

Limits

This is a material estimator only. It does not design reinforcement, compressive strength, subbase depth, drainage, or structural loads.

Sources and further reading

• Wolfram MathWorld: Cuboid - the rectangular-box volume (length x width x height) behind the slab formula.
• NIST Guide to the SI, Appendix B: Conversion Factors - reference for the unit conversions used here, including 12 inches = 1 foot for depth and 27 cubic feet = 1 cubic yard.
• QUIKRETE Concrete Mix (No. 1101) product page - manufacturer source for the premix bag yields (about 0.30 cu ft for 40 lb, 0.45 cu ft for 60 lb, and 0.60 cu ft for 80 lb); always confirm against the printed bag label before ordering.