Calculate cubic yards and bags of concrete needed for slabs, columns, and footings.
Concrete Calculator is a free online tool that helps you calculate cubic yards and bags of concrete needed for slabs, columns, and footings quickly and accurately. Whether you're a student, professional, or just need a quick answer, this calculator provides instant results with clear explanations. All calculations run locally in your browser — no data is stored or transmitted.
Standard pre-mixed concrete bags yield: 40 lb bag = 0.30 cubic feet, 60 lb bag = 0.45 cubic feet, 80 lb bag = 0.60 cubic feet. To convert to cubic yards (what ready-mix trucks sell by), divide cubic feet by 27. For large projects over 1–2 cubic yards, ordering ready-mix concrete is almost always more cost-effective than bags.
For general-purpose concrete, the standard mix ratio is 1:2:3 — 1 part cement, 2 parts sand, 3 parts aggregate (gravel) by volume. A stronger 4000 PSI mix uses 1:1.5:2.5. Adding more water makes concrete easier to pour but weakens it. For structural projects, footings, or anything below grade, always consult local building codes for the required concrete strength (PSI).
Break your project into basic shapes (slabs, columns, footings) and calculate each separately using this tool. Add all volumes together. Always add at least 10% for waste, spillage, and uneven subgrade. For driveways, the standard thickness is 4 inches; for heavy vehicles, use 5–6 inches. For patios, 3.5–4 inches is typical. Order slightly more than you need — running short mid-pour is costly.