.concrete-calculator-wrapper {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 20px;
background: #f9f9f9;
border: 1px solid #e0e0e0;
border-radius: 8px;
}
.calc-header {
text-align: center;
margin-bottom: 25px;
}
.calc-header h2 {
color: #333;
margin: 0;
}
.calc-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
.input-group {
margin-bottom: 15px;
}
.input-group label {
display: block;
font-weight: 600;
margin-bottom: 5px;
color: #444;
}
.input-group input {
width: 100%;
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.dual-input {
display: flex;
gap: 10px;
}
.dual-input div {
flex: 1;
}
.calc-btn-container {
grid-column: 1 / -1;
text-align: center;
margin-top: 10px;
}
.calc-btn {
background-color: #d35400;
color: white;
border: none;
padding: 12px 30px;
font-size: 18px;
font-weight: bold;
border-radius: 5px;
cursor: pointer;
transition: background 0.3s;
}
.calc-btn:hover {
background-color: #a04000;
}
#calc-results {
grid-column: 1 / -1;
background: #fff;
border: 2px solid #d35400;
padding: 20px;
border-radius: 8px;
margin-top: 20px;
display: none;
}
.result-row {
display: flex;
justify-content: space-between;
padding: 10px 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: #222;
font-size: 1.1em;
}
.article-content {
max-width: 800px;
margin: 40px auto;
line-height: 1.6;
color: #333;
}
.article-content h2 {
color: #d35400;
margin-top: 30px;
}
.article-content h3 {
color: #555;
}
.article-content ul {
margin-bottom: 20px;
}
@media (max-width: 600px) {
.calc-grid {
grid-template-columns: 1fr;
}
}
function calculateConcrete() {
// Get Inputs
var lenFt = parseFloat(document.getElementById("lenFt").value) || 0;
var lenIn = parseFloat(document.getElementById("lenIn").value) || 0;
var widFt = parseFloat(document.getElementById("widFt").value) || 0;
var widIn = parseFloat(document.getElementById("widIn").value) || 0;
var thick = parseFloat(document.getElementById("thickness").value) || 0;
var waste = parseFloat(document.getElementById("wasteFactor").value) || 0;
// Validation
if (thick === 0) {
alert("Please enter a thickness greater than 0.");
return;
}
if ((lenFt === 0 && lenIn === 0) || (widFt === 0 && widIn === 0)) {
alert("Please enter valid dimensions for length and width.");
return;
}
// Logic: Convert all to feet
var totalLenFeet = lenFt + (lenIn / 12);
var totalWidFeet = widFt + (widIn / 12);
var totalThickFeet = thick / 12;
// Logic: Calculate Volume in Cubic Feet
var volCuFtRaw = totalLenFeet * totalWidFeet * totalThickFeet;
// Logic: Apply Waste Factor
var wasteMultiplier = 1 + (waste / 100);
var volCuFtTotal = volCuFtRaw * wasteMultiplier;
// Logic: Convert to Cubic Yards (27 cu ft = 1 cu yd)
var volCuYdsTotal = volCuFtTotal / 27;
// Logic: Calculate Bags
// Standard yields: 80lb bag ~= 0.6 cu ft, 60lb bag ~= 0.45 cu ft
var bags80 = volCuFtTotal / 0.6;
var bags60 = volCuFtTotal / 0.45;
// Update DOM
document.getElementById("resYards").innerText = volCuYdsTotal.toFixed(2);
document.getElementById("resFeet").innerText = volCuFtTotal.toFixed(2);
document.getElementById("resBags80").innerText = Math.ceil(bags80);
document.getElementById("resBags60").innerText = Math.ceil(bags60);
// Show results
document.getElementById("calc-results").style.display = "block";
}
How to Calculate Concrete for Slabs
Whether you are pouring a patio, a driveway, or a foundation footing, knowing exactly how much concrete to order is crucial. Ordering too little results in structural weaknesses (cold joints) and costly delays, while ordering too much is a waste of money and labor. This concrete slab calculator helps you determine the precise volume required in cubic yards and cubic feet, as well as the estimated number of pre-mixed bags needed for smaller DIY projects.
The Concrete Calculation Formula
To calculate the volume of concrete needed for a rectangular slab, you use the standard volume formula:
Length × Width × Thickness = Volume
However, the challenge lies in the units. Construction measurements are often taken in a mix of feet and inches, while concrete is sold by the Cubic Yard. Our calculator handles these conversions automatically:
- Step 1: Convert all dimensions to feet. (e.g., 4 inches = 0.33 feet).
- Step 2: Multiply Length (ft) × Width (ft) × Thickness (ft) to get Cubic Feet.
- Step 3: Divide Cubic Feet by 27 to get Cubic Yards.
Pre-Mix Bags vs. Ready Mix Truck
Once you have your total volume, you need to decide how to buy the concrete:
1. Bagged Concrete (DIY)
For small projects (usually under 2 cubic yards), buying pre-mixed bags (like Quikrete or Sakrete) is often more economical.
- 80lb Bags: The most common size. You need approximately 45 bags to make 1 cubic yard.
- 60lb Bags: Easier to handle but more expensive per volume. You need approximately 60 bags to make 1 cubic yard.
2. Ready Mix Truck
For projects exceeding 2 cubic yards, ordering a "ready mix" truck is standard. It saves immense physical labor. Be aware that most delivery companies have a minimum order (often 1 to 3 yards) and may charge "short load fees" for small amounts.
Why Add a Waste Margin?
The "Waste Factor" in our calculator defaults to 5%. In the real world, the ground is rarely perfectly flat, and forms may bow slightly under the weight of wet concrete. Some material also gets left in the mixer or spilled.
- Flat, Even Ground: Add 5% safety margin.
- Uneven Excavation: Add 10% safety margin.
It is always cheaper to buy a few extra bags or order slightly more than to run out halfway through the pour.