.concrete-calculator-wrapper {
max-width: 800px;
margin: 0 auto;
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
color: #333;
line-height: 1.6;
}
.calc-box {
background-color: #f9f9f9;
border: 1px solid #e0e0e0;
border-radius: 8px;
padding: 30px;
margin-bottom: 40px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.calc-title {
text-align: center;
margin-bottom: 25px;
color: #2c3e50;
font-size: 24px;
font-weight: 700;
}
.input-group {
margin-bottom: 20px;
display: flex;
flex-direction: column;
}
.input-group label {
font-weight: 600;
margin-bottom: 8px;
color: #444;
}
.input-row {
display: flex;
gap: 20px;
flex-wrap: wrap;
}
.input-col {
flex: 1;
min-width: 200px;
}
.calc-input {
width: 100%;
padding: 12px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.calc-input:focus {
border-color: #3498db;
outline: none;
box-shadow: 0 0 0 3px rgba(52, 152, 219, 0.2);
}
.calc-btn {
width: 100%;
padding: 15px;
background-color: #e67e22;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.2s;
margin-top: 10px;
}
.calc-btn:hover {
background-color: #d35400;
}
#concrete-results {
display: none;
margin-top: 30px;
background-color: #fff;
border: 1px solid #ddd;
border-radius: 6px;
padding: 20px;
}
.result-row {
display: flex;
justify-content: space-between;
padding: 12px 0;
border-bottom: 1px solid #eee;
}
.result-row:last-child {
border-bottom: none;
}
.result-label {
font-weight: 600;
color: #555;
}
.result-value {
font-weight: 700;
color: #2c3e50;
font-size: 18px;
}
.highlight-result {
color: #e67e22;
font-size: 20px;
}
.content-section h2 {
color: #2c3e50;
margin-top: 40px;
border-bottom: 2px solid #e67e22;
padding-bottom: 10px;
display: inline-block;
}
.content-section h3 {
color: #34495e;
margin-top: 25px;
}
.content-section p {
margin-bottom: 15px;
}
.content-section ul {
margin-bottom: 20px;
padding-left: 20px;
}
.content-section li {
margin-bottom: 10px;
}
.error-msg {
color: #c0392b;
text-align: center;
margin-top: 10px;
display: none;
}
function calculateConcrete() {
var length = parseFloat(document.getElementById('slabLength').value);
var width = parseFloat(document.getElementById('slabWidth').value);
var thickness = parseFloat(document.getElementById('slabThickness').value);
var waste = parseFloat(document.getElementById('wasteFactor').value);
var resultsDiv = document.getElementById('concrete-results');
var errorDiv = document.getElementById('error-message');
// Input Validation
if (isNaN(length) || length <= 0 || isNaN(width) || width <= 0 || isNaN(thickness) || thickness <= 0 || isNaN(waste) || waste < 0) {
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
errorDiv.style.display = 'none';
// Calculations
// 1. Convert thickness from inches to feet
var thicknessFeet = thickness / 12;
// 2. Calculate Cubic Feet
var cubicFeet = length * width * thicknessFeet;
// 3. Add Waste Margin
var totalCubicFeet = cubicFeet * (1 + (waste / 100));
// 4. Convert to Cubic Yards (27 cubic feet in 1 cubic yard)
var cubicYards = totalCubicFeet / 27;
// 5. Calculate Bags
// Typical 80lb bag yields ~0.60 cubic feet
// Typical 60lb bag yields ~0.45 cubic feet
var bags80 = Math.ceil(totalCubicFeet / 0.60);
var bags60 = Math.ceil(totalCubicFeet / 0.45);
// Display Results
document.getElementById('res-yards').innerText = cubicYards.toFixed(2) + " yd³";
document.getElementById('res-feet').innerText = totalCubicFeet.toFixed(2) + " ft³";
document.getElementById('res-bags-80').innerText = bags80 + " bags";
document.getElementById('res-bags-60').innerText = bags60 + " bags";
resultsDiv.style.display = 'block';
}
How to Calculate Concrete for a Slab
Planning a patio, driveway, or shed foundation requires accurate measurements to ensure you order enough concrete without wasting money on excess material. This Concrete Slab Calculator helps you determine the exact volume needed in both cubic yards (for truck orders) and pre-mix bags (for DIY projects).
The Concrete Volume Formula
To calculate the concrete volume for a rectangular slab, you use the following geometric formula:
Volume = Length × Width × Thickness
However, the tricky part is that your length and width are usually in feet, while thickness is in inches. To get an accurate result, you must convert the thickness to feet before multiplying:
- Step 1: Measure Length and Width in feet.
- Step 2: Measure Thickness in inches and divide by 12 to get feet (e.g., 4 inches ÷ 12 = 0.33 feet).
- Step 3: Multiply Length × Width × Thickness (in feet) to get Cubic Feet.
- Step 4: Divide Cubic Feet by 27 to get Cubic Yards.
Why Include a Waste Margin?
Concrete projects rarely go exactly according to plan. Several factors can affect the actual amount of material you need:
- Uneven Subgrade: If your ground isn't perfectly level, some areas will be thicker than others.
- Spillage: Some concrete is lost during mixing or transport.
- Form Deflection: Wooden forms may bow slightly outward under the weight of wet concrete.
We recommend adding a 5% to 10% waste margin to your order to account for these variables. It is much better to have a little extra than to run out before the job is finished.
Ordering Redi-Mix vs. Bagged Concrete
For large projects (typically over 1-2 cubic yards), it is usually more cost-effective and efficient to order "Redi-Mix" concrete delivered by a truck. For smaller pads, sidewalks, or post holes, buying pre-mixed bags (60lb or 80lb) from a hardware store is the standard approach.
Rule of Thumb: One cubic yard of concrete weighs approximately 4,000 lbs. That equals roughly forty-five 60lb bags or thirty-four 80lb bags!