Material Calculator

Planning a new concrete slab for a patio, shed foundation, or walkway? Accurately calculating the amount of concrete needed is crucial to avoid over-ordering (and wasting money) or under-ordering (and causing delays). This calculator helps you determine the precise volume of concrete required for your project, taking into account common dimensions and even a waste factor.

Understanding Concrete Volume

Concrete is typically ordered and sold by the cubic yard. A cubic yard is a volume measurement equivalent to a cube that is 3 feet long, 3 feet wide, and 3 feet high (3ft x 3ft x 3ft = 27 cubic feet). When pouring a slab, you're essentially creating a rectangular prism, and its volume is calculated by multiplying its length, width, and thickness.

Why a Waste Factor?

It's almost always a good idea to include a small waste factor in your concrete order. This accounts for several real-world scenarios:

• Uneven Subgrade: The ground beneath your slab might not be perfectly level, leading to variations in thickness.
• Spillage: Some concrete might be spilled during pouring or finishing.
• Formwork Imperfections: Forms might not be perfectly square or plumb, leading to slight overfills.
• Settling: Concrete can settle slightly, requiring a bit more to achieve the desired level.

A typical waste factor ranges from 5% to 10%, but for very rough or uneven sites, you might consider slightly more. Our calculator defaults to 10% but allows you to adjust it.

How to Use the Concrete Slab Calculator

Simply enter the dimensions of your concrete slab into the fields below. The calculator will then provide you with the estimated cubic yards and cubic feet of concrete you'll need.

Concrete Slab Calculator

Results will appear here.

function calculateConcrete() { var slabLength = parseFloat(document.getElementById('slabLength').value); var slabWidth = parseFloat(document.getElementById('slabWidth').value); var slabThickness = parseFloat(document.getElementById('slabThickness').value); var wasteFactor = parseFloat(document.getElementById('wasteFactor').value); var resultDiv = document.getElementById('concreteResult'); resultDiv.innerHTML = "; // Clear previous results if (isNaN(slabLength) || slabLength <= 0) { resultDiv.innerHTML = 'Please enter a valid positive number for Slab Length.'; return; } if (isNaN(slabWidth) || slabWidth <= 0) { resultDiv.innerHTML = 'Please enter a valid positive number for Slab Width.'; return; } if (isNaN(slabThickness) || slabThickness <= 0) { resultDiv.innerHTML = 'Please enter a valid positive number for Slab Thickness.'; return; } if (isNaN(wasteFactor) || wasteFactor < 0) { resultDiv.innerHTML = 'Please enter a valid non-negative number for Waste Factor.'; return; } // Convert thickness from inches to feet var thicknessFeet = slabThickness / 12; // Calculate volume in cubic feet var volumeCubicFeet = slabLength * slabWidth * thicknessFeet; // Convert cubic feet to cubic yards (1 cubic yard = 27 cubic feet) var volumeCubicYards = volumeCubicFeet / 27; // Apply waste factor var adjustedVolumeCubicYards = volumeCubicYards * (1 + wasteFactor / 100); var adjustedVolumeCubicFeet = volumeCubicFeet * (1 + wasteFactor / 100); resultDiv.innerHTML = 'Estimated Concrete Needed:' + " + adjustedVolumeCubicYards.toFixed(2) + ' cubic yards' + '(' + adjustedVolumeCubicFeet.toFixed(2) + ' cubic feet)' + 'This includes a ' + wasteFactor.toFixed(0) + '% waste factor.'; }

Example Calculation

Let's say you're pouring a concrete patio that is 15 feet long, 12 feet wide, and 6 inches thick. You want to include a 10% waste factor.

1. Length: 15 feet
2. Width: 12 feet
3. Thickness: 6 inches (which is 0.5 feet)
4. Waste Factor: 10%

The calculation would be:

• Volume in cubic feet = 15 ft * 12 ft * 0.5 ft = 90 cubic feet
• Volume in cubic yards = 90 cubic feet / 27 cubic feet/yard = 3.33 cubic yards
• Applying 10% waste factor: 3.33 cubic yards * (1 + 0.10) = 3.33 * 1.10 = 3.66 cubic yards

So, you would need to order approximately 3.66 cubic yards of concrete for this patio.

Tips for Ordering Concrete

• Round Up: Always round up your concrete order to the nearest half or full cubic yard, as concrete suppliers typically don't deliver in smaller increments. For example, if you need 3.66 cubic yards, order 4 cubic yards.
• Confirm with Supplier: Double-check your calculations and discuss your project with your concrete supplier. They can offer advice on specific mixes and delivery logistics.
• Prepare Thoroughly: Ensure your forms are securely built, level, and oiled (if reusable) before the concrete truck arrives. Have all your tools and manpower ready.
• Consider Reinforcement: Depending on the slab's purpose, you might need rebar or wire mesh for reinforcement. This calculator only estimates concrete volume, not reinforcement materials.

Using this calculator will help you get a precise estimate for your concrete needs, making your project planning smoother and more cost-effective.