.calculator-wrapper {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 0 auto;
background: #fff;
padding: 20px;
border-radius: 8px;
box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}
.calc-header {
text-align: center;
margin-bottom: 30px;
background: #2c3e50;
color: white;
padding: 20px;
border-radius: 8px 8px 0 0;
margin: -20px -20px 20px -20px;
}
.calc-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
@media (max-width: 600px) {
.calc-grid {
grid-template-columns: 1fr;
}
}
.input-group {
margin-bottom: 15px;
}
.input-group label {
display: block;
margin-bottom: 5px;
font-weight: 600;
color: #333;
}
.input-group input, .input-group select {
width: 100%;
padding: 10px;
border: 1px solid #ddd;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.input-group .unit {
font-size: 0.85em;
color: #666;
margin-top: 2px;
display: block;
}
.btn-calc {
width: 100%;
background: #e67e22;
color: white;
border: none;
padding: 15px;
font-size: 18px;
font-weight: bold;
border-radius: 4px;
cursor: pointer;
transition: background 0.3s;
margin-top: 10px;
}
.btn-calc:hover {
background: #d35400;
}
.results-area {
margin-top: 30px;
background: #f8f9fa;
padding: 20px;
border-radius: 4px;
border-left: 5px solid #27ae60;
display: none;
}
.result-row {
display: flex;
justify-content: space-between;
margin-bottom: 10px;
padding-bottom: 10px;
border-bottom: 1px solid #e9ecef;
}
.result-row:last-child {
border-bottom: none;
}
.result-label {
font-weight: 600;
color: #555;
}
.result-value {
font-weight: bold;
color: #2c3e50;
}
.highlight-result {
font-size: 1.2em;
color: #27ae60;
}
.calc-article {
margin-top: 50px;
line-height: 1.6;
color: #444;
}
.calc-article h2 {
color: #2c3e50;
border-bottom: 2px solid #e67e22;
padding-bottom: 10px;
margin-top: 30px;
}
.calc-article h3 {
color: #34495e;
margin-top: 25px;
}
.calc-article ul {
padding-left: 20px;
}
.calc-article li {
margin-bottom: 10px;
}
.error-msg {
color: #c0392b;
text-align: center;
display: none;
margin-top: 10px;
}
Please enter valid dimensions for Length, Width, and Thickness.
Project Estimates
Total Volume Required:
0 Cubic Yards
Volume in Cubic Feet:
0 ft³
If using 80lb Premix Bags:
0 Bags
Estimated Cost (80lb):
$0.00
If using 60lb Premix Bags:
0 Bags
Estimated Cost (60lb):
$0.00
How to Calculate Concrete for a Slab
Whether you are pouring a patio, a driveway, or a shed foundation, calculating the correct amount of concrete is crucial. Ordering too little can lead to structural weaknesses called "cold joints," while ordering too much is a waste of money.
The Concrete Formula
To determine the volume of concrete needed, you must calculate the cubic footage of the area and convert it to cubic yards (the standard unit for bulk concrete delivery) or the number of pre-mixed bags.
The basic formula is:
Length (ft) × Width (ft) × Thickness (ft) = Cubic Feet
Note: Since thickness is usually measured in inches, divide the inches by 12 to get feet.
Bag Yields
If you are mixing concrete yourself using pre-mixed bags from a hardware store, here are the standard yields:
- 80lb Bag: Yields approximately 0.60 cubic feet.
- 60lb Bag: Yields approximately 0.45 cubic feet.
- 40lb Bag: Yields approximately 0.30 cubic feet.
Factors Affecting Your Calculation
1. The Sub-Base
Concrete should never be poured directly onto dirt. A 4-inch layer of compacted gravel is recommended for drainage and stability. If your sub-base is uneven, you will need more concrete than the theoretical calculation suggests.
2. Waste Margin
Professional contractors always add a safety margin to their calculations. Spillage during the pour, slight variations in the wooden forms, and uneven ground can eat up volume quickly. We recommend adding 5% to 10% extra material to be safe.
3. Thickness Standards
- 4 Inches: Standard for sidewalks, patios, and garage floors for passenger cars.
- 5-6 Inches: Recommended for driveways holding heavier trucks or RVs.
- 6+ Inches: Heavy-duty industrial foundations.
Frequently Asked Questions
How many bags of concrete make a yard?
It takes approximately 45 bags of 80lb concrete or 60 bags of 60lb concrete to equal one cubic yard (27 cubic feet). Note that one cubic yard of concrete weighs roughly 4,000 lbs, so ensure your vehicle can handle the load if transporting it yourself.
Should I mix bags or order a truck?
As a rule of thumb, if your project requires more than 1 cubic yard (about 45 of the 80lb bags), it is often more economical and physically easier to order ready-mix concrete from a truck delivery service.
function calculateConcrete() {
// Get Input Values
var length = document.getElementById('slabLength').value;
var width = document.getElementById('slabWidth').value;
var thickInches = document.getElementById('slabThickness').value;
var waste = document.getElementById('wasteMargin').value;
var cost80 = document.getElementById('priceBag80').value;
var cost60 = document.getElementById('priceBag60').value;
// DOM Elements for results
var resultsDiv = document.getElementById('resultsArea');
var errorDiv = document.getElementById('errorDisplay');
var resYards = document.getElementById('resCubicYards');
var resFeet = document.getElementById('resCubicFeet');
var resB80 = document.getElementById('resBags80');
var resB60 = document.getElementById('resBags60');
var resC80 = document.getElementById('resCost80');
var resC60 = document.getElementById('resCost60');
var rowC80 = document.getElementById('rowCost80');
var rowC60 = document.getElementById('rowCost60');
// Validation
if (length === "" || width === "" || thickInches === "" || isNaN(length) || isNaN(width) || isNaN(thickInches)) {
errorDiv.style.display = "block";
resultsDiv.style.display = "none";
return;
}
// Parse Floats
var l = parseFloat(length);
var w = parseFloat(width);
var t = parseFloat(thickInches);
var margin = parseFloat(waste);
if (l <= 0 || w <= 0 || t 0) {
var totalCost80 = bags80 * parseFloat(cost80);
resC80.innerText = totalCost80.toFixed(2);
rowC80.style.display = "flex";
} else {
rowC80.style.display = "none";
}
if (cost60 && !isNaN(cost60) && parseFloat(cost60) > 0) {
var totalCost60 = bags60 * parseFloat(cost60);
resC60.innerText = totalCost60.toFixed(2);
rowC60.style.display = "flex";
} else {
rowC60.style.display = "none";
}
// Show Result Box
resultsDiv.style.display = "block";
}