*Calculation includes the selected waste factor to account for spillage and uneven subgrades. Labor is not included.
function calculateConcrete() {
var length = parseFloat(document.getElementById("slabLength").value);
var width = parseFloat(document.getElementById("slabWidth").value);
var thickness = parseFloat(document.getElementById("slabThickness").value);
var price = parseFloat(document.getElementById("pricePerYard").value);
var waste = parseFloat(document.getElementById("wastePercent").value);
// Validation
if (isNaN(length) || isNaN(width) || isNaN(thickness) || length <= 0 || width <= 0 || thickness 0) {
totalCost = totalYards * price;
}
// Display Results
document.getElementById("resYards").innerHTML = totalYards.toFixed(2) + " cu. yards";
document.getElementById("resBags").innerHTML = bagsNeeded + " bags (80lb)";
if (totalCost > 0) {
document.getElementById("resCost").innerHTML = "$" + totalCost.toFixed(2);
} else {
document.getElementById("resCost").innerHTML = "Enter price to calculate";
}
document.getElementById("resultBox").style.display = "block";
}
Understanding Concrete Slab Calculations
Planning a new patio, driveway, or shed foundation requires accurate material estimation. Ordering too little concrete can result in "cold joints" that weaken the structure, while ordering too much wastes money. This Concrete Slab Cost Calculator helps you determine the exact volume required in cubic yards and provides an estimated cost based on local ready-mix prices.
How to Calculate Cubic Yards for Concrete
The formula for calculating concrete volume is relatively straightforward, but unit conversions can be tricky. Here is the step-by-step logic used in this tool:
Convert Dimensions: Ensure all measurements are in feet. Since thickness is usually measured in inches, divide the inches by 12 (e.g., 4 inches = 0.33 feet).
Calculate Volume in Cubic Feet: Multiply Length × Width × Thickness (in feet).
Convert to Cubic Yards: There are 27 cubic feet in one cubic yard. Divide the total cubic feet by 27.
Add Waste Margin: It is industry standard to add 5-10% extra material to account for spillage, over-excavation, or uneven subgrades.
Typical Concrete Thickness Applications
Choosing the right thickness is crucial for the durability of your slab:
4 Inches: Standard for residential sidewalks, patios, and garage floors used for passenger vehicles.
5-6 Inches: Recommended for driveways that accommodate heavier SUVs, trucks, or RVs.
6+ Inches: Heavy-duty commercial applications or areas supporting heavy machinery.
Premix Bags vs. Ready-Mix Truck
For small projects (typically under 2 cubic yards), buying 80lb or 60lb bags of premix concrete from a hardware store is often more economical. For larger projects, ordering a ready-mix truck is usually cheaper per yard and saves significant labor. As a rule of thumb, one cubic yard of concrete weighs approximately 4,000 lbs, which is roughly equivalent to forty-five 80lb bags.