Concrete Calculator

Concrete is sold by the cubic yard for ready-mix delivery and by the 60-lb or 80-lb bag for small hand-mixed jobs. One cubic yard weighs about 4,000 pounds and fills a 10×10-foot area poured 4 inches thick. Residential projects under 2–3 cubic yards are typically mixed by hand or with a rented mixer; anything larger is cheaper and faster with a ready-mix truck, which delivers precisely the volume ordered and saves significant labor.

Slab thickness is the most important variable in concrete projects and the most common source of expensive mistakes. A typical patio, walkway, or the footings under a deck or fence posts needs 4 inches of concrete; a garage slab needs 4–6 inches, or more if parking heavy vehicles; a structural foundation requires 8 inches or more with rebar. Getting thickness wrong means a slab that cracks under load within a few years. Always pour on a compacted gravel base of 4–6 inches to improve drainage and prevent frost heave — in cold climates, frost pushing up an unprotected slab is one of the leading causes of premature concrete failure.

Add 5–10% waste to any concrete order for spills, uneven subgrade, and overpour at form edges. For bag mixing, plan on about 45 bags of 80-lb concrete per cubic yard. Ready-mix in the US typically costs $150–$200 per cubic yard plus a delivery charge, and most trucks have a 1-yard minimum order. If your project falls between volumes, order a full yard rather than mixing the remainder by hand — the labor cost of hand-mixing those last few cubic feet rarely justifies the savings. Fresh concrete must be kept moist for at least 3 days after pouring to cure properly and develop full strength.