Concrete Yard Calculator

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Concrete Yard Calculator
Rectangular Slab (L x W x D)Circular Slab or Column (D x H)Concrete Wall (L x H x T)
Volume Result:
Total Concrete Required: Cubic Yards
function toggleInputs(){var type = document.getElementById('calc_type').value;if(type === 'circ'){document.getElementById('rectInputs').style.display='none';document.getElementById('circInputs').style.display='table';} else {document.getElementById('rectInputs').style.display='table';document.getElementById('circInputs').style.display='none';}}function calculateConcrete(){var type = document.getElementById('calc_type').value;var waste = parseFloat(document.getElementById('waste').value) || 0;var cubicFeet = 0;if(type === 'rect' || type === 'wall'){var l = parseFloat(document.getElementById('length').value);var w = parseFloat(document.getElementById('width').value);var t = parseFloat(document.getElementById('thickness').value);if(isNaN(l) || isNaN(w) || isNaN(t)){alert('Please enter valid dimensions');return;}cubicFeet = l * w * (t / 12);} else {var d = parseFloat(document.getElementById('diameter').value);var h = parseFloat(document.getElementById('depth_circ').value);if(isNaN(d) || isNaN(h)){alert('Please enter valid dimensions');return;}var radius = d / 2;cubicFeet = Math.PI * Math.pow(radius, 2) * (h / 12);}var totalCuFt = cubicFeet * (1 + (waste / 100));var cubicYards = totalCuFt / 27;document.getElementById('yardValue').innerHTML = cubicYards.toFixed(2);var bagHtml = "";if(document.getElementById('show_bags').checked){var bags80 = Math.ceil(totalCuFt / 0.6);var bags60 = Math.ceil(totalCuFt / 0.45);var bags40 = Math.ceil(totalCuFt / 0.3);bagHtml = "Pre-mix Bag Requirements:
";bagHtml += "• 80lb Bags: approx. " + bags80 + " bags
";bagHtml += "• 60lb Bags: approx. " + bags60 + " bags
";bagHtml += "• 40lb Bags: approx. " + bags40 + " bags
";bagHtml += "*Estimates include " + waste + "% waste factor.";}document.getElementById('bagResults').innerHTML = bagHtml;document.getElementById('answer').style.display = 'block';}

How to Use the Concrete Yard Calculator

Whether you are pouring a patio, a driveway, or setting posts for a new fence, knowing exactly how much material to order is critical. This concrete yard calculator simplifies the complex conversions between feet, inches, and cubic yards, ensuring you don't run out of concrete mid-pour or overspend on excess material.

To get an accurate estimate, follow these steps:

Select Shape
Choose between a rectangular slab (standard for patios and driveways) or a circular slab (common for decorative areas or post holes).
Enter Dimensions
Input the length and width in feet, but enter the thickness in inches. Most residential slabs are 4 to 6 inches thick.
Waste Margin
We recommend a standard 10% waste margin. This accounts for spillage, variations in the subgrade, and material left in the mixer or pump.

The Formula: How Cubic Yards are Calculated

In the United States, concrete is sold by the cubic yard. Since most project measurements are taken in feet and inches, the math requires a few steps of conversion. The fundamental concept is that 1 cubic yard equals 27 cubic feet.

Volume in Cubic Yards = [(Length × Width × (Thickness ÷ 12)) ÷ 27] × (1 + Waste Percentage)

  • Thickness ÷ 12: Converts inches into feet so all units are consistent.
  • Length × Width × Depth: Calculates the total volume in cubic feet.
  • ÷ 27: The final conversion step because 3ft x 3ft x 3ft = 27ft³.

Example Calculation

Scenario: You want to pour a 12-foot by 15-foot backyard patio that is 4 inches thick. You want to include a 10% waste factor to be safe.

Step-by-step solution:

  1. Convert thickness to feet: 4 inches / 12 = 0.333 feet.
  2. Calculate cubic feet: 12ft × 15ft × 0.333ft = 60 cubic feet.
  3. Convert to cubic yards: 60 / 27 = 2.22 cubic yards.
  4. Add 10% waste: 2.22 × 1.10 = 2.44 cubic yards.
  5. Final Result: You should order 2.5 cubic yards from the ready-mix supplier.

Buying Concrete: Ready-Mix vs. Bags

Depending on the size of your project, you have two primary options for obtaining concrete. This concrete yard calculator helps you decide which route is more cost-effective.

When to Use Bags

If your project is smaller than 1 cubic yard (roughly 45 bags of 80lb concrete), buying bags from a local hardware store is usually more affordable. It allows you to work at your own pace without the pressure of a ticking clock from a delivery truck. Common bag sizes include:

  • 80lb bag: Yields 0.60 cubic feet.
  • 60lb bag: Yields 0.45 cubic feet.
  • 40lb bag: Yields 0.30 cubic feet.

When to Use Ready-Mix

For projects larger than 1 cubic yard, ready-mix delivery is highly recommended. Mixing 50+ bags by hand is physically exhausting and often results in inconsistent concrete quality. Most ready-mix companies have a minimum order (usually 1 to 3 yards) and may charge a "short load" fee if you order less than their standard truck capacity.

Common Questions

How much does a yard of concrete weigh?

Standard concrete weighs approximately 4,000 pounds (2 tons) per cubic yard. When planning your project, ensure your subgrade and forms can handle this significant weight.

How many 80lb bags are in a yard?

There are 45 bags of 80lb pre-mix concrete in one cubic yard. If you are calculating for a 2-yard project, you would need 90 bags. This is why many contractors switch to delivery for anything over a single yard.

Why is it called a "yard" instead of a "cubic yard"?

In the construction industry, "yard" is commonly used as shorthand for cubic yard. While a yard is technically a unit of length (3 feet), in the context of concrete, mulch, or gravel, it almost always refers to volume.

Should I round up my order?

Yes. It is much cheaper to have a small amount of concrete left over than to be short by half a yard. If you are short, you face the risk of a "cold joint," where the first section of concrete begins to harden before the rest arrives, creating a permanent structural weakness and an unsightly line.

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