.calc-container {
max-width: 600px;
margin: 20px auto;
padding: 30px;
background: #f8f9fa;
border: 1px solid #e9ecef;
border-radius: 8px;
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.calc-row {
display: flex;
flex-wrap: wrap;
margin-bottom: 20px;
justify-content: space-between;
}
.calc-col {
flex: 0 0 48%;
display: flex;
flex-direction: column;
}
.calc-full {
flex: 0 0 100%;
}
.calc-label {
font-weight: 600;
margin-bottom: 8px;
color: #333;
font-size: 14px;
}
.calc-input, .calc-select {
padding: 12px;
border: 1px solid #ced4da;
border-radius: 4px;
font-size: 16px;
transition: border-color 0.15s;
}
.calc-input:focus, .calc-select:focus {
border-color: #007bff;
outline: 0;
}
.calc-btn {
width: 100%;
padding: 14px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: 700;
cursor: pointer;
transition: background-color 0.2s;
text-transform: uppercase;
letter-spacing: 0.5px;
}
.calc-btn:hover {
background-color: #0056b3;
}
.calc-results {
margin-top: 30px;
padding-top: 20px;
border-top: 2px dashed #dee2e6;
display: none;
}
.result-box {
background: #fff;
padding: 15px;
border-radius: 6px;
border-left: 5px solid #28a745;
margin-bottom: 15px;
box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}
.result-label {
font-size: 13px;
color: #6c757d;
text-transform: uppercase;
letter-spacing: 1px;
margin-bottom: 5px;
}
.result-value {
font-size: 24px;
font-weight: 800;
color: #212529;
}
.result-sub {
font-size: 14px;
color: #555;
margin-top: 5px;
}
.error-msg {
color: #dc3545;
font-size: 14px;
margin-top: 10px;
display: none;
text-align: center;
}
@media (max-width: 500px) {
.calc-col {
flex: 0 0 100%;
margin-bottom: 15px;
}
}
.article-content {
max-width: 800px;
margin: 40px auto;
font-family: Georgia, 'Times New Roman', Times, serif;
line-height: 1.8;
color: #333;
}
.article-content h2 {
font-family: -apple-system, sans-serif;
color: #2c3e50;
margin-top: 40px;
font-size: 28px;
border-bottom: 2px solid #eee;
padding-bottom: 10px;
}
.article-content h3 {
font-family: -apple-system, sans-serif;
color: #444;
margin-top: 30px;
font-size: 22px;
}
.article-content p {
margin-bottom: 20px;
font-size: 18px;
}
.article-content ul {
margin-bottom: 25px;
padding-left: 20px;
}
.article-content li {
margin-bottom: 10px;
font-size: 18px;
}
.highlight-box {
background-color: #e8f4fd;
padding: 20px;
border-radius: 8px;
margin: 30px 0;
}
function calculateConcrete() {
// 1. Get Input Values
var length = document.getElementById("slabLength").value;
var width = document.getElementById("slabWidth").value;
var thickness = document.getElementById("slabThickness").value;
var quantity = document.getElementById("slabQuantity").value;
var waste = document.getElementById("wasteMargin").value;
var errorDiv = document.getElementById("errorDisplay");
var resultsDiv = document.getElementById("resultsArea");
// 2. Validate Inputs
if (length === "" || width === "" || thickness === "" || quantity === "") {
errorDiv.style.display = "block";
resultsDiv.style.display = "none";
return;
}
var lenNum = parseFloat(length);
var widNum = parseFloat(width);
var thickNum = parseFloat(thickness);
var qtyNum = parseFloat(quantity);
var wasteNum = parseFloat(waste);
if (lenNum <= 0 || widNum <= 0 || thickNum <= 0 || qtyNum <= 0) {
errorDiv.style.display = "block";
errorDiv.innerHTML = "Values must be greater than zero.";
resultsDiv.style.display = "none";
return;
}
// 3. Perform Calculations
// Formula: (L x W x (T/12)) = Cubic Feet
var thicknessInFeet = thickNum / 12;
var cubicFeetPerItem = lenNum * widNum * thicknessInFeet;
var totalCubicFeet = cubicFeetPerItem * qtyNum * wasteNum;
// Cubic Yards = Cubic Feet / 27
var totalCubicYards = totalCubicFeet / 27;
// Bag Calculations
// Standard yield: 80lb bag ~= 0.6 cubic feet
// Standard yield: 60lb bag ~= 0.45 cubic feet
var bags80 = Math.ceil(totalCubicFeet / 0.6);
var bags60 = Math.ceil(totalCubicFeet / 0.45);
// 4. Update UI
errorDiv.style.display = "none";
resultsDiv.style.display = "block";
document.getElementById("resYards").innerHTML = totalCubicYards.toFixed(2);
document.getElementById("resFeet").innerHTML = totalCubicFeet.toFixed(2);
document.getElementById("resBags80").innerHTML = bags80;
document.getElementById("resBags60").innerHTML = bags60;
}
Concrete Slab Calculator & Project Guide
Planning a patio, driveway, or shed foundation? Accurate calculations are the foundation of any successful concrete project. This Concrete Slab Calculator helps you determine exactly how many cubic yards or pre-mix bags you need, factoring in standard waste margins to prevent you from running short mid-pour.
Quick Tip: Always calculate for a 5-10% waste margin. Uneven subgrades and spillage during the pour often consume more material than a perfect mathematical volume calculation suggests.
How to Calculate Concrete Volume
Concrete is sold by volume, specifically in Cubic Yards. To calculate this manually, you need to convert all your measurements to feet and use the following formula:
The Formula
(Length in feet × Width in feet × Thickness in feet) / 27 = Cubic Yards
Since slab thickness is usually measured in inches, you must divide the thickness inches by 12 before multiplying. For example, a 4-inch slab is 0.33 feet thick.
Example Calculation
Let's say you are pouring a patio that is 10 feet long, 10 feet wide, and 4 inches thick.
- Convert thickness: 4″ ÷ 12 = 0.33′
- Calculate Cubic Feet: 10 × 10 × 0.33 = 33 cubic feet
- Convert to Cubic Yards: 33 ÷ 27 = 1.22 cubic yards
Pre-Mix Bags vs. Ready-Mix Truck
Once you have your total volume, you need to decide how to buy the concrete. This usually depends on the size of the project.
When to Use Bags (60lb or 80lb)
Bagged concrete (like Quikrete or Sakrete) is ideal for small projects requiring less than 1 cubic yard. It is labor-intensive as you must mix it yourself.
- 80lb Bags: Yield approximately 0.6 cubic feet.
- 60lb Bags: Yield approximately 0.45 cubic feet.
When to Order a Truck
If your project requires more than 1 cubic yard, ordering a ready-mix truck is usually more cost-effective and saves immense physical labor. Most concrete delivery companies have a minimum order (often 1 yard + short load fee, or 3-4 yards standard).
Recommended Thickness Guide
The thickness of your slab determines its structural integrity. Use these standard guidelines:
- 4 Inches: Standard for walkways, patios, and residential sidewalks.
- 5-6 Inches: Required for driveways, garage floors, or slabs supporting hot tubs.
- 6+ Inches: Necessary for heavy equipment or commercial driveways.
Frequently Asked Questions
Does this calculator account for rebar or gravel?
No, this calculator determines the volume of wet concrete needed. You should calculate gravel base (usually 4 inches deep) separately using similar dimensions.
How much water do I add to 80lb bags?
Generally, an 80lb bag requires about 3 to 4 quarts of water. Start with less water and add slowly to reach a consistency similar to thick oatmeal. Too much water weakens the concrete.
What is the "Waste Margin"?
The waste margin accounts for spillage, material stuck in the mixer, and uneven ground (subgrade). If your ground is perfectly flat, 5% is safe. If you are pouring on uneven dirt, choose 10%.