80 lb (0.60 cu ft)
60 lb (0.45 cu ft)
40 lb (0.30 cu ft)
Calculation Summary:
Total Volume Required: 0 Cubic Yards
Total Cubic Feet: 0 cu. ft.
Number of Bags Needed: 0 bags
Estimated Material Cost: $0.00
function calculateConcrete() {
var length = parseFloat(document.getElementById('slabLength').value);
var width = parseFloat(document.getElementById('slabWidth').value);
var thicknessInches = parseFloat(document.getElementById('slabThickness').value);
var waste = parseFloat(document.getElementById('wasteFactor').value) / 100;
var bagWeight = parseFloat(document.getElementById('bagSize').value);
var pricePerBag = parseFloat(document.getElementById('costPerBag').value) || 0;
if (isNaN(length) || isNaN(width) || isNaN(thicknessInches) || length <= 0 || width <= 0 || thicknessInches <= 0) {
alert('Please enter valid positive numbers for length, width, and thickness.');
return;
}
// Convert thickness to feet
var thicknessFeet = thicknessInches / 12;
// Calculate Cubic Feet
var cubicFeet = length * width * thicknessFeet;
// Add wastage
var totalCubicFeet = cubicFeet * (1 + waste);
// Convert to Cubic Yards (1 cubic yard = 27 cubic feet)
var cubicYards = totalCubicFeet / 27;
// Bag coverage yields
var bagYield = 0;
if (bagWeight === 80) bagYield = 0.60;
else if (bagWeight === 60) bagYield = 0.45;
else if (bagWeight === 40) bagYield = 0.30;
var totalBags = Math.ceil(totalCubicFeet / bagYield);
var totalCost = totalBags * pricePerBag;
// Display results
document.getElementById('resVolumeYards').innerText = cubicYards.toFixed(2);
document.getElementById('resVolumeFeet').innerText = totalCubicFeet.toFixed(2);
document.getElementById('resTotalBags').innerText = totalBags;
document.getElementById('resTotalCost').innerText = '$' + totalCost.toFixed(2);
document.getElementById('resultsArea').style.display = 'block';
}
How to Calculate Concrete Volume
Calculating the correct amount of concrete for a slab, patio, or driveway is essential to avoid overspending or running out of material mid-pour. The standard formula for volume is:
4 Inches: Standard for walkways, patios, and residential pool decks.
5-6 Inches: Recommended for driveways that will hold heavy SUVs or trucks.
8+ Inches: Heavy-duty commercial use or machinery pads.
Concrete Bag Yields
Most DIY projects use pre-mixed bags. Here is a quick reference for the volume yield of standard bag sizes:
Bag Weight
Volume Yield (Cubic Feet)
80 lb Bag
0.60 cu. ft.
60 lb Bag
0.45 cu. ft.
40 lb Bag
0.30 cu. ft.
Why Include a Wastage Factor?
Professional contractors always include a 10% waste factor. This accounts for variations in the subgrade (ground not being perfectly flat), spillage, or material left inside the mixer. It is much cheaper to have a few extra bags left over than to have a cold joint because you ran out of concrete before finishing the slab.
Example Calculation
If you are pouring a 10ft x 10ft patio that is 4 inches thick: