Calculate cubic yards and pre-mix bags needed for your project
Please enter valid dimensions.
Project Estimation
Volume Required:0 Cubic Yards
Volume (Cubic Feet):0 cu ft
Pre-Mix Bag Options
80lb Bags Needed:0 Bags
60lb Bags Needed:0 Bags
Estimated Truck Cost:$0.00
function calculateConcrete() {
// Get Input Values
var length = parseFloat(document.getElementById('slabLength').value);
var width = parseFloat(document.getElementById('slabWidth').value);
var thick = parseFloat(document.getElementById('slabThickness').value);
var waste = parseFloat(document.getElementById('wasteFactor').value);
var price = parseFloat(document.getElementById('pricePerYard').value);
// Validation
var errorDiv = document.getElementById('errorMsg');
var resultDiv = document.getElementById('calcResults');
if (isNaN(length) || isNaN(width) || isNaN(thick) || length <= 0 || width <= 0 || thick 0) {
totalCost = cubicYards * price;
showCost = true;
}
// Display Results
resultDiv.style.display = 'block';
document.getElementById('resYards').innerHTML = cubicYards.toFixed(2) + " Cubic Yards";
document.getElementById('resFeet').innerHTML = cubicFeetTotal.toFixed(2) + " cu ft";
document.getElementById('res80lb').innerHTML = bags80 + " Bags";
document.getElementById('res60lb').innerHTML = bags60 + " Bags";
if (showCost) {
document.getElementById('costSection').style.display = 'block';
document.getElementById('resCost').innerHTML = "$" + totalCost.toFixed(2);
} else {
document.getElementById('costSection').style.display = 'none';
}
}
How to Calculate Concrete Needed for a Slab
Planning a driveway, patio, or shed foundation requires accurate volume calculations. Ordering too little concrete results in expensive delays and "cold joints," while ordering too much is a waste of money. This concrete slab calculator helps you determine the exact volume required in cubic yards and the equivalent number of pre-mix bags (60lb or 80lb) for smaller DIY projects.
The Concrete Formula
To calculate the concrete volume, you need to determine the volume of the space in cubic feet and then convert it to cubic yards, which is the standard unit for ordering from a ready-mix truck.
The basic formula is:
Step 1: Convert thickness from inches to feet (Divide inches by 12).
Step 3: Divide Cubic Feet by 27 to get Cubic Yards.
Why Include Waste?
Professional contractors always include a "margin of safety" or waste factor, typically between 5% and 10%. This accounts for:
Spillage during transport and pouring.
Uneven subgrade (dips in the ground) that increase slab thickness in certain spots.
Form settling or bowing under the weight of the wet concrete.
For a perfectly flat, well-compacted subgrade, 5% is sufficient. For uneven ground or complex shapes, consider 10%.
Truck vs. Bags: When to Switch?
When should you mix it yourself versus ordering a truck? generally:
Under 1 Cubic Yard: It is usually more economical to buy bags (60lb or 80lb) and mix it yourself using a wheelbarrow or a rented electric mixer. Note that 1 cubic yard requires roughly 45 bags of 80lb mix—that is a lot of labor!
Over 1 Cubic Yard: Ordering a ready-mix truck becomes time and cost-effective. However, be aware of "short load fees" for orders under 4-5 yards depending on your local supplier.
Standard Slab Thicknesses
Not sure how thick your slab should be? Here are common standards:
4 Inches: Standard for walkways, patios, and residential garage floors.
5-6 Inches: Required for driveways that handle heavier vehicles or RVs.
6+ Inches: Heavy-duty commercial aprons or foundations supporting heavy machinery.