#concrete-slab-calculator-wrapper .calc-container {
background: #f8f9fa;
border: 1px solid #e9ecef;
border-radius: 8px;
padding: 30px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
margin-bottom: 40px;
}
#concrete-slab-calculator-wrapper h2 {
color: #2c3e50;
border-bottom: 2px solid #e67e22;
padding-bottom: 10px;
margin-top: 30px;
}
#concrete-slab-calculator-wrapper .form-group {
margin-bottom: 20px;
}
#concrete-slab-calculator-wrapper label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #495057;
}
#concrete-slab-calculator-wrapper input[type="number"] {
width: 100%;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box; /* Important for responsiveness */
}
#concrete-slab-calculator-wrapper .calc-btn {
background-color: #e67e22;
color: white;
border: none;
padding: 15px 30px;
font-size: 18px;
font-weight: bold;
border-radius: 4px;
cursor: pointer;
width: 100%;
transition: background-color 0.3s;
}
#concrete-slab-calculator-wrapper .calc-btn:hover {
background-color: #d35400;
}
#concrete-slab-calculator-wrapper #concResult {
margin-top: 25px;
padding: 20px;
background-color: #ffffff;
border: 1px solid #dee2e6;
border-radius: 4px;
display: none;
}
#concrete-slab-calculator-wrapper .result-row {
display: flex;
justify-content: space-between;
padding: 10px 0;
border-bottom: 1px solid #eee;
}
#concrete-slab-calculator-wrapper .result-row:last-child {
border-bottom: none;
}
#concrete-slab-calculator-wrapper .result-label {
font-weight: 600;
color: #555;
}
#concrete-slab-calculator-wrapper .result-value {
font-weight: 700;
color: #2c3e50;
font-size: 1.1em;
}
#concrete-slab-calculator-wrapper .highlight {
color: #e67e22;
}
#concrete-slab-calculator-wrapper .content-section p {
line-height: 1.6;
margin-bottom: 15px;
}
#concrete-slab-calculator-wrapper .content-section ul {
margin-bottom: 20px;
padding-left: 20px;
}
#concrete-slab-calculator-wrapper .content-section li {
margin-bottom: 10px;
line-height: 1.6;
}
@media (min-width: 600px) {
#concrete-slab-calculator-wrapper .input-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
}
function calculateConcreteSlab() {
// Get inputs
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);
// Validation
if (isNaN(length) || length <= 0 || isNaN(width) || width <= 0 || isNaN(thickness) || thickness <= 0) {
document.getElementById('concResult').style.display = 'block';
document.getElementById('concResult').innerHTML = 'Please enter valid dimensions for Length, Width, and Thickness.';
return;
}
if (isNaN(waste) || waste < 0) {
waste = 0;
}
// Calculation Logic
// 1. Calculate base volume in cubic feet. Thickness is in inches, so divide by 12.
var thicknessInFeet = thickness / 12;
var cubicFeetBase = length * width * thicknessInFeet;
// 2. Add waste factor
var totalCubicFeet = cubicFeetBase * (1 + (waste / 100));
// 3. Convert to Cubic Yards (27 cubic feet per cubic yard)
var cubicYards = totalCubicFeet / 27;
// 4. Calculate Bags
// 80lb bag yields approx 0.6 cubic feet
// 60lb bag yields approx 0.45 cubic feet
var bags80 = Math.ceil(totalCubicFeet / 0.60);
var bags60 = Math.ceil(totalCubicFeet / 0.45);
// Formatting Output
var resultHTML = '';
resultHTML += '
How to Calculate Concrete for a Slab
Calculating the correct amount of concrete for a slab is critical to the success of your project. Ordering too little can result in "cold joints" and structural weaknesses, while ordering too much wastes money and creates disposal issues. This calculator determines the volume based on the standard engineering formula:
Volume (Cubic Feet) = Length × Width × (Thickness ÷ 12)
Since concrete is typically sold by the Cubic Yard or by the bag (for smaller projects), converting this number is essential. There are 27 cubic feet in one cubic yard.
Why Include a Waste Margin?
Professional contractors always include a waste margin, typically between 5% and 10%. This accounts for:
- Spillage during the pour.
- Uneven subgrade (ground) depth.
- Settling of the concrete.
- Material remaining in the mixer or wheelbarrow.
For a perfectly flat, well-compacted subgrade, 5% is usually sufficient. If you are pouring on uneven ground, consider increasing the margin to 10%.
Understanding Bag Counts (Pre-Mix)
If you are using pre-mixed concrete bags (common for patios, walkways, and small shed foundations), the yield depends on the bag weight:
- 80lb Bags: Yield approximately 0.60 cubic feet per bag.
- 60lb Bags: Yield approximately 0.45 cubic feet per bag.
Note: Always round up to the nearest whole bag to ensure you don't run short.
Calculation Results
'; resultHTML += '';
resultHTML += 'Total Volume Needed:';
resultHTML += '' + totalCubicFeet.toFixed(2) + ' ft³';
resultHTML += '
';
resultHTML += '';
resultHTML += 'Cubic Yards (Truck Order):';
resultHTML += '' + cubicYards.toFixed(2) + ' yd³';
resultHTML += '
';
resultHTML += '';
resultHTML += 'If buying pre-mix bags:';
resultHTML += '';
resultHTML += '80lb Bags Required:';
resultHTML += '' + bags80 + ' bags';
resultHTML += '
';
resultHTML += '';
resultHTML += '60lb Bags Required:';
resultHTML += '' + bags60 + ' bags';
resultHTML += '
';
// Display Result
var resultContainer = document.getElementById('concResult');
resultContainer.style.display = 'block';
resultContainer.innerHTML = resultHTML;
}