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Concrete Calculator
Calculate cubic yards, weight, bags, and cost for slabs, footings, columns, circular pads, steps, and curb & gutter — instantly, right in your browser.
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Quick Answer
To calculate concrete for a slab, multiply length × width × thickness (in feet), then divide by 27 to convert cubic feet into cubic yards.
yd³ = (L ft × W ft × T ft) ÷ 27
Choose Your Project Type
01 / Slab
Slab Calculator
For driveways, patios, and flatwork. Enter length, width, and thickness to get exact yardage.
02 / Footing
Footing Calculator
For wall and foundation footings. Enter length, width, and depth to size your pour.
03 / Column
Column Calculator
For round piers and sonotube columns. Enter diameter, height, and quantity.
04 / Circular Slab
Circular Slab Calculator
For round pads, silos, and tree rings. Enter diameter and thickness.
05 / Steps
Steps Calculator
For concrete stairs and stoops. Enter width, rise, run, and step count.
06 / Curb & Gutter
Curb & Gutter Calculator
For linear curb and gutter runs. Enter length and cross-section dimensions.
08 / Cost
Concrete Cost Calculator
Estimate total cost from cubic yards and your local price per yard.
09 / All Shapes
All Calculators
Switch between all six shapes instantly in the interactive tool above.
Understanding Your Concrete Order
Every concrete pour starts with the same question: how much material do you actually need? Volume is the foundation of that answer, but a finished order depends on more than just length, width, and depth. The mix design, the aggregate blend, and the amount of Portland cement in the recipe all affect how the material behaves once it is placed, while the compressive strength of the mix — usually expressed in PSI — determines whether a standard residential blend or a higher-strength mix is appropriate for the job.
For most homeowners, the practical choice comes down to ready-mix or bagged concrete. Ready-mix is batched at a plant and delivered by truck, which suits larger pours where a consistent, single batch matters. Bagged concrete is mixed by hand or with a small mixer on-site, and it remains the more sensible option for footings, fence posts, and other small-volume repairs where a full truck delivery would not be practical. Either way, ordering a little more than the raw math suggests is standard practice: a waste factor of 5–10% covers subgrade irregularities, form leakage, and the material lost to spillage during a pour.
Reinforcement is the other half of the equation. Slabs, footings, and columns that carry structural loads typically call for rebar or wire mesh embedded within the pour, sized and spaced according to the project’s engineering requirements. Combined with the right thickness for the application — thinner for a patio, thicker for a driveway subject to vehicle loads — these choices determine how the finished slab performs over time. The calculator above handles the volume math for six common shapes, converting your measurements into cubic yards, weight, and bag counts so you can move from planning to ordering with a single, clear number.
Learn More
Frequently Asked Questions
How much concrete do I need for a slab?
Multiply the slab’s length by width by thickness, all measured in feet, then divide by 27 to convert cubic feet into cubic yards. Add 5–10% for waste, spillage, and uneven subgrade before ordering.
How many bags of concrete do I need per cubic yard?
A standard 80 lb bag yields about 0.6 cubic feet of mixed concrete, a 60 lb bag about 0.45 cubic feet, and a 40 lb bag about 0.3 cubic feet. Since one cubic yard equals 27 cubic feet, that works out to roughly 45 bags at 80 lb, 60 bags at 60 lb, or 90 bags at 40 lb per cubic yard.
How much does a cubic yard of concrete cost?
Ready-mix pricing varies by region, mix strength, and delivery minimums, so there is no single national number. Ask your local ready-mix supplier for a current quote and use the cost calculator above to convert that price per yard into a total for your project.
How much does concrete weigh?
Standard concrete weighs approximately 150 pounds per cubic foot, or roughly 4,050 pounds — just over two tons — per cubic yard. Lightweight mixes can weigh less, so check your mix design if weight matters for structural loading.
What’s the difference between ready-mix and bagged concrete?
Ready-mix concrete is batched at a plant and delivered by truck, which is typically more economical for pours larger than about one cubic yard. Bagged concrete is mixed on-site with a mixer or wheelbarrow and is more practical for small jobs like footings, posts, or repairs.
How much waste or overage should I add to my order?
Most contractors add 5–10% overage to account for subgrade irregularities, form leakage, and spillage. Rougher excavation, thicker slabs, or a first-time DIY pour can justify pushing that closer to 10–15%.
What thickness should a concrete slab be?
A typical residential patio or walkway slab is 4 inches thick, while driveways and areas that carry vehicle loads are usually poured 5–6 inches thick. Local codes and soil conditions can change these numbers, so confirm thickness with your project’s engineer or building department.
How do I calculate concrete for round columns or footings?
Use the formula for a cylinder: pi times radius squared times height, where radius is half the diameter. The column calculator above does this automatically and also multiplies by quantity if you’re pouring more than one pier.