Estimate the volume of concrete and bags needed for your project.
0% (Exact)
5% (Recommended)
10% (High Safety)
Project Totals
Total Volume:0 ft³
Cubic Yards Needed:0 yd³
80lb Bags of Premix:0 bags
60lb Bags of Premix:0 bags
Estimated Cost (Bags):–
Estimated Cost (Truck):–
function calculateConcrete() {
// 1. Get Inputs
var length = parseFloat(document.getElementById('slabLength').value);
var width = parseFloat(document.getElementById('slabWidth').value);
var thickness = parseFloat(document.getElementById('slabThickness').value);
var wastePercent = parseFloat(document.getElementById('wasteFactor').value);
var bagPrice = parseFloat(document.getElementById('bagPrice').value);
var truckPrice = parseFloat(document.getElementById('truckPrice').value);
// 2. Validation
if (isNaN(length) || isNaN(width) || isNaN(thickness)) {
alert("Please enter valid numbers for Length, Width, and Thickness.");
return;
}
if (length <= 0 || width <= 0 || thickness <= 0) {
alert("Dimensions must be greater than zero.");
return;
}
// 3. Logic Calculation
// Convert thickness from inches to feet
var thicknessFeet = thickness / 12;
// Calculate cubic feet
var volumeCuFt = length * width * thicknessFeet;
// Add waste margin
var multiplier = 1 + (wastePercent / 100);
var totalCuFt = volumeCuFt * multiplier;
// Convert to cubic yards (27 cubic feet in 1 cubic yard)
var totalYards = totalCuFt / 27;
// Calculate Bags
// 1 cubic foot of concrete usually requires about 1.66 80lb bags or 2.22 60lb bags.
// More precise yield:
// 80lb bag yields ~0.60 cubic feet
// 60lb bag yields ~0.45 cubic feet
var bags80 = Math.ceil(totalCuFt / 0.60);
var bags60 = Math.ceil(totalCuFt / 0.45);
// Calculate Costs
var costBags = 0;
var costTruck = 0;
var displayCostBags = "-";
var displayCostTruck = "-";
if (!isNaN(bagPrice)) {
costBags = bags80 * bagPrice;
displayCostBags = "$" + costBags.toFixed(2);
}
if (!isNaN(truckPrice)) {
// Usually redi-mix has a minimum (e.g. 1 yard), but we will calculate strictly by volume for now
// If total yards < 1, usually they charge a short load fee, but we'll stick to simple math
var chargedYards = totalYards < 1 ? 1 : totalYards; // Simple assumption logic
costTruck = chargedYards * truckPrice;
// Actually, let's just do pure math: yards * price
costTruck = totalYards * truckPrice;
displayCostTruck = "$" + costTruck.toFixed(2);
}
// 4. Update UI
document.getElementById('resVolumeCuFt').innerHTML = totalCuFt.toFixed(2) + " ft³";
document.getElementById('resVolumeYards').innerHTML = totalYards.toFixed(2) + " yd³";
document.getElementById('resBags80').innerHTML = bags80 + " bags";
document.getElementById('resBags60').innerHTML = bags60 + " bags";
document.getElementById('resCostBags').innerHTML = displayCostBags;
document.getElementById('resCostTruck').innerHTML = displayCostTruck;
// Show results
document.getElementById('results').style.display = "block";
}
How to Calculate Concrete for Slabs
Whether you are pouring a patio, a driveway, or footings for a deck, calculating the correct amount of concrete is crucial. Underestimating can lead to a "cold joint" if you run out midway, while overestimating wastes money and leaves you with heavy material to dispose of.
This Concrete Slab Calculator helps you determine exactly how many cubic yards or pre-mix bags (60lb or 80lb) you need for your project.
The Concrete Formula
To calculate the concrete volume, you treat the slab as a rectangular prism. The formula is:
Volume = Length × Width × Thickness
Note: Ensure all units are consistent. Since length and width are usually in feet and thickness is in inches, you must convert the thickness to feet by dividing by 12.
Step-by-Step Calculation:
Measure the Length and Width in feet.
Measure the Thickness in inches. Standard patios are 4 inches; driveways are typically 5 to 6 inches.
Convert to Cubic Yards (for truck delivery): Divide cubic feet by 27. 33 ÷ 27 = 1.22 cubic yards.
Should I Mix Bags or Order a Truck?
Deciding between buying bags at a hardware store or ordering a ready-mix truck depends on the volume:
Under 1 Cubic Yard: It is usually cheaper and easier to buy 60lb or 80lb bags and mix them yourself in a wheelbarrow or portable mixer.
Over 1 Cubic Yard: Ordering a truck is often more efficient. Mixing by hand becomes labor-intensive quickly. Note that many ready-mix companies have a "short load" fee for orders under 3-4 yards.
Important Tips for Your Concrete Pour
1. The Waste Factor: Never order the exact amount calculated geometrically. Ground surfaces are rarely perfectly level, and some concrete may spill or remain in the mixer. We recommend adding 5-10% extra to your calculation to be safe.
2. Prepare the Subgrade: Ensure your soil is compacted. For best results, place 2-4 inches of gravel (base rock) under the concrete to assist with drainage and prevent cracking.
3. Use Rebar or Mesh: For driveways or heavy-load areas, reinforce your slab with steel rebar or wire mesh to increase tensile strength.