How Much Concrete Do You Need?
Enter your slab, column, or step dimensions and get cubic yards, bags, and a full material list.
Concrete Estimate
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How to Calculate How Much Concrete You Need
To calculate concrete for a slab, multiply the length × width × thickness (in feet). Divide by 27 to convert cubic feet to cubic yards. For a 4-inch-thick slab, divide the inch measurement by 12 first.
Example:A 10ft × 10ft slab that's 4 inches thick: 10 × 10 × (4/12) = 33.3 cubic feet ÷ 27 = 1.23 cubic yards.
For columns (Sonotube), use the cylinder formula: π × r² × height. For steps, each step is calculated as a rectangular prism that increases in height with each successive step.
Always add 5–10% extrato your order. Grade variations, form flex, and spillage mean you'll use more than the math says. Running short during a pour is far more expensive than ordering a little extra.
When to use bags vs. ready-mix: For projects under 1 cubic yard, bags are practical. Above 1 cubic yard, ready-mix delivery is more economical and produces a more consistent result.
Frequently Asked Questions
How much concrete do I need for a 10x10 slab?
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A 10x10 slab that's 4 inches thick requires about 1.23 cubic yards of concrete. With 10% waste, order 1.4 cubic yards. That's about 23 bags of 80-lb concrete mix for a DIY project.
How many bags of concrete do I need?
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An 80-lb bag covers about 0.6 cubic feet. Calculate your volume in cubic feet, add 10% for waste, then divide by 0.6. For a small 4x4x4-inch slab, you need about 1-2 bags.
How much does concrete cost per cubic yard?
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Ready-mix concrete costs $130-$180 per cubic yard delivered, depending on location and mix design. High-strength (4,000+ PSI) costs more. For small jobs, 80-lb bags cost about $7.50 each.
What PSI concrete should I use?
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3,000 PSI is standard for residential sidewalks and patios. Use 4,000+ PSI for driveways, garage floors, and any surface bearing vehicle traffic or heavy loads.
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