Please enter valid numeric values for all dimensions.
Total Volume Required:0 cu. yards
Total Cubic Feet:0 cu. ft
Premix Bags (80lb):0 bags
Premix Bags (60lb):0 bags
Estimated Material Cost:$0.00
Understanding Concrete Slab Calculations
Planning a construction project involves precise material estimation to ensure structural integrity and budget control. Whether you are pouring a patio, a driveway, or a foundation for a shed, calculating the correct amount of concrete is the critical first step. This guide helps you understand the metrics behind the calculator above.
The Core Formula
Concrete is sold by volume, typically in cubic yards. To determine how much you need, you must convert your slab dimensions into a unified volume measurement.
Step 1: Calculate the volume in cubic feet: Length (ft) × Width (ft) × (Thickness (in) ÷ 12)
For example, a 10×10 foot patio that is 4 inches thick equates to approximately 1.23 cubic yards before accounting for waste.
Why Include a Waste Margin?
Professional contractors never order the exact mathematical amount of concrete. Spillage, uneven subgrades, and form spreading can alter the volume required. We recommend a 5% to 10% safety margin. It is far cheaper to pay for a little extra concrete than to pay for a "short load" delivery fee or attempt to patch a drying slab with a second batch.
Choosing the Right Thickness
The depth of your slab depends heavily on its intended use:
4 Inches: Standard for residential sidewalks, patios, and garage floors (for passenger cars).
5-6 Inches: Recommended for driveways hosting heavy trucks, RVs, or machinery.
6+ Inches: Heavy industrial use or floating foundations.
Premix Bags vs. Ready-Mix Truck
If your project requires less than 1 cubic yard (approx. 45-50 bags of 80lb mix), mixing it yourself using bagged concrete is often more cost-effective. For volumes greater than 1-2 cubic yards, ordering a ready-mix truck is usually preferred to ensure consistency and save labor.
function calculateConcrete() {
// 1. Get Input Values
var lengthEl = document.getElementById('slab-length');
var widthEl = document.getElementById('slab-width');
var thickEl = document.getElementById('slab-thickness');
var wasteEl = document.getElementById('waste-margin');
var priceEl = document.getElementById('price-per-yard');
var errorEl = document.getElementById('csc-error-msg');
var resultDiv = document.getElementById('csc-results');
// 2. Parse Values
var length = parseFloat(lengthEl.value);
var width = parseFloat(widthEl.value);
var thickness = parseFloat(thickEl.value);
var wastePercent = parseFloat(wasteEl.value);
var pricePerYard = parseFloat(priceEl.value);
// 3. Validation
if (isNaN(length) || length <= 0 || isNaN(width) || width <= 0 || isNaN(thickness) || thickness 0) {
totalCost = totalCubicYards * pricePerYard;
}
// 5. Display Results
document.getElementById('res-yards').innerHTML = totalCubicYards.toFixed(2) + " cu. yards";
document.getElementById('res-feet').innerHTML = totalCubicFeet.toFixed(2) + " cu. ft";
document.getElementById('res-bags-80').innerHTML = Math.ceil(bags80) + " bags";
document.getElementById('res-bags-60').innerHTML = Math.ceil(bags60) + " bags";
if (totalCost > 0) {
document.getElementById('res-cost').innerHTML = "$" + totalCost.toFixed(2);
} else {
document.getElementById('res-cost').innerHTML = "Enter price to calculate";
}
resultDiv.style.display = 'block';
}