Total Volume Required (incl. waste):0.00 cubic yards
Estimated Truck Delivery Cost:$0.00
Alternative: DIY Premix Bags
80lb Bags Needed:0 bags
Estimated DIY Bag Cost:$0.00
Note: Calculations include the specified waste margin to account for spillage and uneven subgrades. Prices vary by location.
How to Calculate Concrete Slab Costs
Planning a new driveway, patio, or garage foundation requires precise measurements to avoid ordering too much expensive material or, worse, running short in the middle of a pour. Our Concrete Slab Cost Calculator helps you determine exactly how many cubic yards of concrete you need and compares the cost of ordering a ready-mix truck versus mixing bags yourself.
The Concrete Volume Formula
To calculate the concrete required for a slab, you must determine the volume in cubic feet and then convert it to cubic yards, which is the standard unit for pricing and delivery in the United States.
The basic formula is:
Area (Square Feet) = Length (ft) × Width (ft)
Volume (Cubic Feet) = Area × (Thickness (in) ÷ 12)
Volume (Cubic Yards) = Volume (Cubic Feet) ÷ 27
Understanding Thickness Requirements
The thickness of your slab depends entirely on its intended use:
4 Inches: Standard for residential sidewalks, patios, and steps. Suitable for foot traffic.
5-6 Inches: Recommended for driveways and garage floors that will support passenger vehicles and light trucks.
8+ Inches: Required for heavy equipment areas or commercial foundations.
The "Waste Factor" Explained
Experienced contractors never order the exact mathematical volume. Subgrades are rarely perfectly flat, and forms may bow slightly under the weight of wet concrete. We recommend adding a 5% to 10% safety margin (waste factor) to ensure you have enough material to finish the job correctly without cold joints.
Ready-Mix Truck vs. Premix Bags
When should you order a truck versus buying bags from a home improvement store?
DIY Bags (80lb or 60lb): Best for small projects under 1 cubic yard (approx. 45 bags of 80lb mix). It is labor-intensive but cheaper for small volumes.
Ready-Mix Truck: Best for any project over 1 cubic yard. Although there may be a "short load fee" for small orders, the consistency of the mix and the ease of pouring directly from the chute make it the superior choice for driveways and large patios.
Average Concrete Costs
While prices fluctuate based on region and fuel costs, you can generally expect to pay between $125 and $150 per cubic yard for ready-mix concrete delivered. Premix bags typically cost between $4.50 and $6.50 per 80lb bag. Always verify current local pricing before creating your final budget.
function calculateConcrete() {
// 1. Get Input Values
var length = parseFloat(document.getElementById('slabLength').value);
var width = parseFloat(document.getElementById('slabWidth').value);
var thicknessInches = parseFloat(document.getElementById('slabThickness').value);
var wastePercent = parseFloat(document.getElementById('wasteFactor').value);
var pricePerYard = parseFloat(document.getElementById('pricePerYard').value);
var pricePerBag = parseFloat(document.getElementById('bagPrice').value);
// 2. Validate Inputs
if (isNaN(length) || isNaN(width) || isNaN(thicknessInches) || length <= 0 || width <= 0) {
alert("Please enter valid positive numbers for dimensions.");
return;
}
if (isNaN(pricePerYard)) pricePerYard = 0;
if (isNaN(pricePerBag)) pricePerBag = 0;
if (isNaN(wastePercent)) wastePercent = 0;
// 3. Perform Calculations
// Area in Square Feet
var areaSqFt = length * width;
// Thickness in Feet
var thicknessFt = thicknessInches / 12;
// Volume in Cubic Feet
var volumeCuFt = areaSqFt * thicknessFt;
// Convert to Cubic Yards (1 yard = 27 cubic feet)
var volumeCuYards = volumeCuFt / 27;
// Add Waste Factor
var wasteMultiplier = 1 + (wastePercent / 100);
var totalYardsNeeded = volumeCuYards * wasteMultiplier;
var totalCuFtNeeded = volumeCuFt * wasteMultiplier;
// Calculate Truck Cost
var totalTruckCost = totalYardsNeeded * pricePerYard;
// Calculate Bags Needed
// Standard 80lb bag yields approx 0.60 cubic feet
// Or roughly 45 bags per cubic yard.
// Specific yield: 80lbs / ~133lbs/cf density = ~0.6 cu ft
// A common rule of thumb is 1 cubic yard = 3600 lbs (approx)
// 3600 / 80 = 45 bags.
var bagsNeeded = Math.ceil(totalYardsNeeded * 45);
var totalBagCost = bagsNeeded * pricePerBag;
// 4. Update UI
document.getElementById('resArea').innerHTML = areaSqFt.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 2}) + " sq ft";
document.getElementById('resYards').innerHTML = totalYardsNeeded.toFixed(2) + " cubic yards";
document.getElementById('resTruckCost').innerHTML = "$" + totalTruckCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resBags').innerHTML = bagsNeeded + " bags";
document.getElementById('resBagCost').innerHTML = "$" + totalBagCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Show Results Container
document.getElementById('resultsArea').style.display = "block";
}