Concrete Calculator

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Calculate the exact amount of concrete you need for any project — whether you're pouring a driveway slab, setting footings for a deck, or filling column forms. Enter your dimensions and our free concrete calculator instantly tells you how many cubic yards and how many 40lb, 60lb, or 80lb bags you need, with a 10% waste factor included.

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Enter Your Measurements

Results

Concrete Needed

1.23

cubic yards

With 10% Overage

1.36

cubic yards

Volume

33.3

cubic feet

80 lb Bags

56

bags

60 lb Bags

75

bags

Cost Estimate

$

per cubic yard

Estimated Cost

$185.19

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Formula

Cubic Yards = (Length ft × Width ft × Depth in ÷ 12) ÷ 27

How to Use This Calculator

How to Use

  1. 1

    Measure the length of your project area in feet — for irregular shapes, break the area into rectangles and calculate each section separately.

  2. 2

    Measure the width of your project area in feet, taking measurements at multiple points and using the average for accuracy.

  3. 3

    Determine the depth (thickness) in inches — standard residential slabs are 4 inches, driveways are 6 inches, and heavy-load areas should be 8 inches or more.

  4. 4

    Review the results, which show cubic yards with a 10% waste factor already added, plus bag counts for 60 lb and 80 lb pre-mix bags.

Frequently Asked Questions

Frequently Asked Questions

How do I calculate how much concrete I need?

To calculate concrete volume, multiply the length by the width by the depth — all in feet. Since depth is usually measured in inches, divide your inch measurement by 12 first. This gives you cubic feet. Divide by 27 to convert to cubic yards. For example, a 10x10 ft slab at 4 inches deep is (10 × 10 × 0.333) ÷ 27 = 1.23 cubic yards. Always add 10% for waste.

How many 80 lb bags of concrete do I need per cubic yard?

You need approximately 45 bags of 80 lb concrete mix to make one cubic yard of concrete. Each 80 lb bag yields about 0.6 cubic feet, and there are 27 cubic feet in a cubic yard. For 60 lb bags, you need about 60 bags per yard. This makes bagged concrete expensive and labor-intensive for large pours — ready-mix is more practical for jobs over one yard.

When should I use bags vs ready-mix concrete?

Use bagged concrete for small projects under 1 cubic yard — things like setting fence posts, filling small footings, or patching repairs. For larger jobs, ready-mix concrete delivered by truck is far more economical and practical. Ready-mix costs approximately $125 to $150 per cubic yard delivered, and a single truck typically delivers 8 to 10 yards. The break-even point where ready-mix becomes cheaper is usually around 1 yard.

What is a 10% waste factor for concrete?

A 10% waste factor accounts for the unavoidable extra concrete you need beyond the theoretical calculated volume. Concrete can be lost to uneven subgrade (your forms may not be perfectly flat), slight spills during the pour, form deflection under the weight of wet concrete, and variations in slab thickness. Always order at least 10% more than your calculated amount — running out mid-pour is a serious problem because you cannot let concrete start setting before the pour is complete.

How long does concrete take to set and cure?

Concrete begins its initial set within 2 to 4 hours of pouring, meaning it becomes firm enough that you cannot work it. It reaches walking strength within 24 to 48 hours under normal conditions (70°F). However, concrete doesn't reach its full design strength (typically 3,000 to 4,000 PSI) until 28 days of curing. Keeping concrete moist during the first week by covering it with wet burlap or plastic sheeting significantly improves final strength.

How thick should a concrete slab be?

Slab thickness depends entirely on what it needs to support. Residential patios, sidewalks, and walkways are typically poured at 4 inches — sufficient for foot traffic and light loads. Driveways and garage floors should be a minimum of 6 inches to handle passenger vehicle weight. Areas that will see heavy trucks, RVs, or equipment should be 8 inches. Foundation slabs are typically 4 to 8 inches depending on structural loads, with thickened edges at footings.
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About This Calculator

Volume is calculated using the formula Length × Width × (Depth ÷ 12) to get cubic feet, then divided by 27 to convert to cubic yards — the unit used by ready-mix suppliers. Bag counts use the Portland Cement Association's standard yields: 80 lb bag = 0.60 cu ft, 60 lb bag = 0.45 cu ft. A 10% waste factor is applied per ACI (American Concrete Institute) best practices to account for spillage, uneven subgrade, and form waste.

Built and maintained by the CalcSmart team. Last updated March 2026.

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