Concrete Slab Calculator
Use this calculator to determine the amount of concrete needed for a slab, patio, or footing. Simply enter the dimensions of your slab, and the calculator will provide the estimated volume in cubic yards, including a recommended waste factor.
function calculateConcreteSlab() {
var lengthFeet = parseFloat(document.getElementById('slabLengthFeet').value);
var widthFeet = parseFloat(document.getElementById('slabWidthFeet').value);
var thicknessInches = parseFloat(document.getElementById('slabThicknessInches').value);
var wasteFactorPercent = parseFloat(document.getElementById('wasteFactorPercent').value);
var resultDiv = document.getElementById('concreteSlabResult');
if (isNaN(lengthFeet) || isNaN(widthFeet) || isNaN(thicknessInches) || isNaN(wasteFactorPercent) ||
lengthFeet <= 0 || widthFeet <= 0 || thicknessInches <= 0 || wasteFactorPercent < 0) {
resultDiv.innerHTML = 'Please enter valid positive numbers for all fields.';
return;
}
// Convert thickness from inches to feet
var thicknessFeet = thicknessInches / 12;
// Calculate volume in cubic feet
var volumeCubicFeet = lengthFeet * widthFeet * thicknessFeet;
// Convert cubic feet to cubic yards (1 cubic yard = 27 cubic feet)
var volumeCubicYards = volumeCubicFeet / 27;
// Apply waste factor
var finalVolumeCubicYards = volumeCubicYards * (1 + wasteFactorPercent / 100);
resultDiv.innerHTML =
'
Estimated Concrete Needed:' +
" + finalVolumeCubicYards.toFixed(2) + ' cubic yards' +
'
(Raw volume: ' + volumeCubicYards.toFixed(2) + ' cubic yards, plus ' + wasteFactorPercent.toFixed(0) + '% waste)';
}
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padding: 25px;
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max-width: 600px;
margin: 20px auto;
border: 1px solid #e0e0e0;
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width: calc(100% – 22px);
padding: 10px;
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border-radius: 5px;
font-size: 1em;
box-sizing: border-box;
}
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margin-top: 30px;
padding: 15px;
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border-radius: 5px;
text-align: center;
font-size: 1.1em;
color: #155724;
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Understanding Concrete Volume for Slabs
Calculating the correct amount of concrete for a slab, patio, or footing is crucial for any construction project. Ordering too little concrete can lead to costly delays and potential cold joints (weak points where new concrete is poured against hardened concrete). Ordering too much results in wasted material and disposal costs.
How to Use the Concrete Slab Calculator:
- Slab Length (feet): Measure the total length of your slab in feet. For irregular shapes, break them down into rectangles and sum the volumes.
- Slab Width (feet): Measure the total width of your slab in feet.
- Slab Thickness (inches): Determine the desired thickness of your slab in inches. Common thicknesses for residential patios and walkways are 4 inches, while driveways might be 6 inches or more.
- Waste Factor (%): This is an important buffer. Concrete projects often encounter slight variations in subgrade, spillage, or measurement inaccuracies. A waste factor of 5-10% is generally recommended to ensure you don't run short.
- Click "Calculate Concrete" to get your estimated volume in cubic yards.
The Calculation Explained:
The calculator works by determining the volume of a rectangular prism. Here's the breakdown:
- Convert Thickness to Feet: Since length and width are in feet, the thickness (entered in inches) is converted to feet by dividing by 12.
- Calculate Volume in Cubic Feet: The volume is then calculated using the formula:
Length (feet) × Width (feet) × Thickness (feet).
- Convert to Cubic Yards: Concrete is typically ordered in cubic yards. There are 27 cubic feet in 1 cubic yard. So, the volume in cubic feet is divided by 27.
- Apply Waste Factor: Finally, the calculated raw volume is increased by the specified waste factor percentage to give you a more realistic order quantity.
Example Calculation:
Let's say you're pouring a concrete patio with the following dimensions:
- Length: 20 feet
- Width: 10 feet
- Thickness: 4 inches
- Waste Factor: 10%
Here's how the calculation would proceed:
- Thickness in feet: 4 inches / 12 = 0.3333 feet
- Volume in cubic feet: 20 feet × 10 feet × 0.3333 feet = 66.66 cubic feet
- Volume in cubic yards: 66.66 cubic feet / 27 = 2.47 cubic yards
- Applying 10% waste factor: 2.47 cubic yards × (1 + 10/100) = 2.47 × 1.10 = 2.72 cubic yards
Based on this, you would need to order approximately 2.75 cubic yards of concrete (often rounded up to the nearest quarter or half yard by suppliers).