Calculate exactly how much concrete you need for slabs, footings, or driveways.
0%
5% (Recommended)
10%
Total Volume (Cubic Yards):0.00
Total Volume (Cubic Feet):0.00
80lb Bags Required:0
60lb Bags Required:0
How to Calculate Concrete Volume
Calculating the volume of concrete needed for a project is a critical conversion step for any construction or DIY job. Concrete is typically measured in cubic yards or cubic feet. To find the volume, you must multiply the surface area (length × width) by the depth (thickness). However, because thickness is usually measured in inches while area is measured in feet, a conversion is required.
The Mathematical Formula
To calculate the cubic yards manually, use the following formula:
((Length in ft × Width in ft × (Thickness in inches / 12)) / 27) = Cubic Yards
Example: A slab that is 10 feet long, 10 feet wide, and 4 inches thick.
1. Convert thickness: 4 / 12 = 0.333 feet.
2. Calculate volume: 10 × 10 × 0.333 = 33.33 cubic feet.
3. Convert to yards: 33.33 / 27 = 1.23 cubic yards.
Why Waste Allowance Matters
In real-world applications, it is rare for a site to be perfectly level or for no concrete to be spilled. Professional contractors typically add a 5% to 10% "waste factor" to their calculations. This ensures that you do not run out of wet concrete mid-pour, which can lead to structural "cold joints."
Bag Count Conversion
If you are buying pre-mixed bags from a hardware store, you need to know the yield of each bag size:
80lb Bag: Yields approximately 0.60 cubic feet.
60lb Bag: Yields approximately 0.45 cubic feet.
Our calculator automatically performs these conversions and rounds up to the nearest whole bag, ensuring your supply list is accurate for the store.
function calculateConcrete() {
var length = parseFloat(document.getElementById('lengthFeet').value);
var width = parseFloat(document.getElementById('widthFeet').value);
var thickness = parseFloat(document.getElementById('thicknessInches').value);
var wastePercent = parseFloat(document.getElementById('spillage').value);
if (isNaN(length) || isNaN(width) || isNaN(thickness) || length <= 0 || width <= 0 || thickness <= 0) {
alert("Please enter valid positive numbers for all dimensions.");
return;
}
// Calculate thickness in feet
var thicknessFt = thickness / 12;
// Calculate base cubic feet
var cubicFeet = length * width * thicknessFt;
// Add waste factor
var totalCubicFeet = cubicFeet * (1 + (wastePercent / 100));
// Convert to cubic yards (1 yard = 27 cubic feet)
var cubicYards = totalCubicFeet / 27;
// Calculate bags
// 80lb bag = 0.6 cubic feet
// 60lb bag = 0.45 cubic feet
var bags80 = Math.ceil(totalCubicFeet / 0.6);
var bags60 = Math.ceil(totalCubicFeet / 0.45);
// Display Results
document.getElementById('resYards').innerText = cubicYards.toFixed(2);
document.getElementById('resFeet').innerText = totalCubicFeet.toFixed(2);
document.getElementById('res80lb').innerText = bags80;
document.getElementById('res60lb').innerText = bags60;
document.getElementById('results').style.display = 'block';
}