Concrete Calculator

How to calculate how much concrete you need

Concrete volume in the US is measured in cubic yards for ready-mix orders and in bags for small pours. One cubic yard equals 27 cubic feet. The right shape formula gets you to that number fast.

Step 1 — Choose your shape

A slab or pad is any flat rectangular pour — a patio, driveway section, or sidewalk. A footing is a deeper, narrower rectangle supporting a wall or post. A column is a cylinder. A circular slab is a round pad for a patio table base or hot tub. Pick the one that matches your project.

Step 2 — Enter your dimensions

Measure length and width in feet. Measure thickness or depth in inches — the calculator converts to feet internally. If your slab is 4 inches thick, that is 0.333 feet. Use a tape measure for actual project dimensions, not estimates.

Step 3 — Read cubic yards and bag count

The result shows cubic yards, which is what ready-mix suppliers charge by. It also shows how many 60 lb and 80 lb bags you need for a bagged concrete job. Before ordering, add 10% to the cubic yard figure to cover spillage and slight measurement error.

Step 4 — Estimate cost

Enter a price per cubic yard if you have a supplier quote. Ready-mix concrete in the US typically runs $125 to $180 per yard depending on region and mix strength. The calculator multiplies your price by the yardage for a quick material estimate. Delivery, pump fees, and finishing are not included.

Concrete volume — cubic yards, cubic feet, and bags

One cubic yard is exactly 27 cubic feet — that is the standard unit ready-mix plants quote. To get there from a slab, multiply length × width × thickness (all in feet) to find cubic feet, then divide by 27. For example, a 10×10 slab at 4 inches thick: thickness in feet is 4 ÷ 12 = 0.333, so volume = 10 × 10 × 0.333 = 33.3 ft³, and 33.3 ÷ 27 = 1.23 yd³.

For tiny pours — a couple of post holes, a small patch, or a single step — bagged mix wins on convenience. Past roughly a cubic yard, calling for ready-mix usually saves money and time. Trucks often carry 8–10 yards per load, and many plants add a short-load fee when you order only a yard or two, so plan batching with a neighbor if you are close to that threshold.

Real pours are messy. The subgrade is rarely perfectly flat, a little mud stays on the wheelbarrow, and forms leak a cup here and there. That is why contractors routinely order about 10% more than the naked math — it beats stopping mid-pour to chase another pallet of bags.

Concrete slab calculator — common project reference

Here are pre-calculated estimates for common residential concrete projects using the same formulas as the calculator above.

Add 10% to all figures before ordering.

How many bags of concrete per cubic yard?

At the usual retail yields, a 60 lb bag is about 0.45 cubic feet and an 80 lb bag is about 0.60 cubic feet. Stacked up, that lands near 60 bags of 60 lb or 45 bags of 80 lb for a full cubic yard. The 80 lb route uses fewer lifts and fewer pieces of torn paper flapping in the wind, which matters more than it sounds on a hot afternoon.

For fence posts, a couple of pads, or a curb patch, grabbing a few bags on the way home is fine. Before you load the truck bed, plug your real dimensions into the calculator so you are not back at the home center during the cure window.

Ready-mix concrete cost in the US

In 2025 most homeowners see $125–$180 per yard for standard 3,000 PSI sidewalk mix, with the coasts and big cities at the top of that band. High-early or 4,000+ PSI structural mixes cost more. If you only need a yard or two, ask about minimum-load charges — they often run $50–$100 before the concrete itself. Weekend pours sometimes carry a dispatcher surcharge too.

For reference, the Concrete Network — Concrete Prices Guide publishes industry data on mix design and concrete properties. For slab design guidance, the QUIKRETE Concrete Mix Reference covers thickness and reinforcement recommendations for residential flatwork.

For other home project estimates, see all tools on the CalcSpring homepage.