About the Concrete Calculator
Concrete is ordered by volume — either in cubic yards for ready-mix truck delivery or by bag count for smaller DIY projects like a fence post footing or small patio slab — and getting that volume calculation wrong is one of the most common and expensive mistakes in a home concrete project.
This calculator converts length, width, and thickness (commonly measured in inches for slab depth) into total cubic feet, then converts that into cubic yards for ready-mix ordering, or an estimated bag count for pre-mixed 80 lb bags, using the standard yield of roughly 0.6 cubic feet per bag.
Frequently Asked Questions
Why should I order extra concrete beyond the calculated amount?
Ground isn't perfectly level, forms aren't perfectly precise, and some material is inevitably lost to spillage during mixing and pouring — a 5-10% buffer is standard practice to avoid running short mid-pour, which can compromise the slab's structural integrity at the seam.
What thickness should I use for a driveway vs. a walkway?
Typical guidance is around 4 inches for walkways and patios, and 5-6 inches for driveways that need to support vehicle weight — though local building codes and soil conditions can affect the recommended thickness for your specific project.
When should I order ready-mix instead of using bagged concrete?
For larger pours (typically more than about 1 cubic yard), ready-mix delivery is usually more practical and often more cost-effective than mixing dozens of bags by hand, while bagged concrete suits smaller projects like post footings or small repairs.