function calculateConcrete() {
// Get input values
var length = parseFloat(document.getElementById('concLength').value);
var width = parseFloat(document.getElementById('concWidth').value);
var thickness = parseFloat(document.getElementById('concThickness').value);
var wastePercent = parseFloat(document.getElementById('concWaste').value);
// Validation
if (isNaN(length) || isNaN(width) || isNaN(thickness)) {
alert("Please enter valid numbers for Length, Width, and Thickness.");
return;
}
if (isNaN(wastePercent)) {
wastePercent = 0;
}
// Calculate Area in Square Feet
var areaSqFt = length * width;
// Calculate Volume in Cubic Feet (Thickness / 12 to convert inches to feet)
var volCuFt = areaSqFt * (thickness / 12);
// Add Waste Margin
var wasteMultiplier = 1 + (wastePercent / 100);
var totalVolCuFt = volCuFt * wasteMultiplier;
// Calculate Cubic Yards (27 cubic feet in 1 cubic yard)
var totalVolYards = totalVolCuFt / 27;
// Calculate Bags
// 60lb bag yields approx 0.45 cubic feet
// 80lb bag yields approx 0.60 cubic feet
var bags60 = Math.ceil(totalVolCuFt / 0.45);
var bags80 = Math.ceil(totalVolCuFt / 0.60);
// Update DOM
document.getElementById('resFeet').innerText = totalVolCuFt.toFixed(2) + " cu. ft.";
document.getElementById('resYards').innerText = totalVolYards.toFixed(2) + " Cubic Yards";
document.getElementById('resBags60').innerText = bags60 + " Bags";
document.getElementById('resBags80').innerText = bags80 + " Bags";
// Show result box
document.getElementById('concResult').style.display = "block";
}
How to Calculate Concrete for Slabs and Footings
Whether you are pouring a new patio, a driveway, or setting footings for a deck, knowing exactly how much concrete to order is crucial. Ordering too little can result in a "cold joint" which weakens the structure, while ordering too much wastes money and creates disposal issues. This Concrete Calculator helps you estimate the volume required in cubic yards and the number of premix bags needed for smaller DIY projects.
Understanding the Formula
The basic formula for concrete volume involves three dimensions: length, width, and thickness. Since concrete is sold by volume (cubic yards) but measured in linear feet and inches, conversion is necessary.
Step 1: Calculate the area in square feet (Length × Width).
Step 2: Convert thickness from inches to feet (Inches ÷ 12).
Step 3: Multiply Area by Thickness to get Cubic Feet.
Step 4: Divide Cubic Feet by 27 to get Cubic Yards.
Bagged Concrete vs. Ready-Mix Truck
For small projects (typically under 1 to 1.5 cubic yards), using bagged concrete (like Quikrete or Sakrete) is often more economical. Common bag sizes include:
60lb Bags: Yield approximately 0.45 cubic feet.
80lb Bags: Yield approximately 0.60 cubic feet.
For larger projects requiring more than 2 cubic yards, ordering a ready-mix truck is usually the standard. Trucks ensure a consistent mix and save immense physical labor required to mix dozens of bags by hand.
Why Include a Waste Margin?
In the construction industry, it is standard practice to order 5% to 10% more material than the exact mathematical calculation. This accounts for:
Spillage during transport and pouring.
Uneven subgrade (ground) depth.
Settling of the concrete.
Our calculator allows you to input a custom waste percentage to ensure you don't run short in the middle of your pour.