Concrete Calculator

Concrete is one of the most essential building materials in construction. Whether you are pouring a simple patio slab, building foundation footings, or setting posts, accurately estimating the amount of concrete you need is critical to avoid waste and unexpected costs.

Concrete is typically sold in cubic yards in the United States, and one cubic yard equals 27 cubic feet. For smaller projects, pre-mixed bags of 60 or 80 pounds are common. A standard 80-pound bag yields approximately 0.6 cubic feet of mixed concrete, while a 60-pound bag yields around 0.45 cubic feet.

When calculating concrete for a slab, multiply the length by width by depth (all in feet), then divide by 27 to convert to cubic yards. Always add 5-10% extra to account for uneven ground, spillage, and form irregularities. For round columns, use the formula: π × radius² × height.

Ready-mix concrete costs $120-$160 per cubic yard on average, while bagged concrete runs about $4-$6 per 80-pound bag. For projects larger than 1 cubic yard, ordering ready-mix from a truck is usually more economical and produces a more consistent result.

Proper preparation is essential for a successful concrete pour. Make sure your forms are level and well-braced, the sub-grade is compacted, and you have enough labor on hand since concrete sets quickly — typically within 30-60 minutes depending on weather conditions.

Regional pricing has a bigger impact on concrete cost than most people expect. In 2026, ready-mix delivered in major metro areas can run $140–$180 per cubic yard, while rural areas may see lower material prices but higher delivery surcharges. Most suppliers add a short-load fee of $40–$60 per yard for orders under 3–4 yards, plus a per-mile delivery charge beyond a set radius. Getting two or three local quotes almost always pays for itself.

The most common estimating mistake is forgetting to convert depth to feet. A 4-inch slab is 0.333 feet deep, not 4 — using inches by accident overestimates the pour twelvefold. The second most common mistake is ignoring sub-grade variation: if your excavation is even half an inch deeper than planned across a large slab, you can need 10–15% more concrete than the ideal calculation suggests, which is exactly why a waste allowance matters.

Reinforcement is not optional for slabs that will carry weight. Welded wire mesh is the minimum for patios and walkways, while driveways and garage floors should use a #4 rebar grid on 18-inch centers. Fiber-reinforced mix can reduce (but not eliminate) surface cracking and is worth the small upcharge for exposed slabs. Whatever reinforcement you choose, keep it in the middle third of the slab's thickness — rebar lying on the sub-grade does almost nothing.

Curing is where good pours go wrong. Concrete does not simply dry out — it hardens through a chemical reaction that needs moisture and time. Keep a new slab damp, or covered with curing blankets or plastic, for the first 3–7 days; a properly cured slab can reach substantially higher final strength than one left to dry out in the sun. Avoid pouring when temperatures will drop below 40°F or climb above 90°F within 24 hours unless you use cold- or hot-weather admixtures.