How to Calculate Freelance Rate Based on Salary

Professional Concrete Calculator

Rectangular Slab / Wall Circular Column / Sonotube

80 lb bags (0.6 cu ft) 60 lb bags (0.45 cu ft) 40 lb bags (0.3 cu ft)

(Standard is 10% to account for spills or uneven subgrade)

Results:

Total Volume: 0 Cubic Yards

Total Volume: 0 Cubic Feet

Number of Bags Needed: 0

function calculateConcrete() { var type = document.getElementById('projectType').value; var length = parseFloat(document.getElementById('lengthInput').value); var width = parseFloat(document.getElementById('widthInput').value); var thick = parseFloat(document.getElementById('thicknessInput').value); var bagType = parseFloat(document.getElementById('bagSize').value); var waste = parseFloat(document.getElementById('wasteInput').value) / 100; if (isNaN(length) || isNaN(thick) || (type === 'slab' && isNaN(width))) { alert('Please enter valid numerical values for all dimensions.'); return; } var volumeCuFt = 0; if (type === 'slab') { // Volume = L (ft) * W (ft) * (T (in) / 12) volumeCuFt = length * width * (thick / 12); } else { // Column: Volume = PI * r^2 * h // thick is Diameter in inches, convert to radius in feet var radiusFt = (thick / 2) / 12; volumeCuFt = Math.PI * Math.pow(radiusFt, 2) * length; } // Add waste var totalCuFt = volumeCuFt * (1 + waste); var totalCuYards = totalCuFt / 27; // Bag coverage based on standard yields var yieldPerBag = 0.6; // Default for 80lb if (bagType === 60) yieldPerBag = 0.45; if (bagType === 40) yieldPerBag = 0.3; var bagsNeeded = Math.ceil(totalCuFt / yieldPerBag); document.getElementById('resYards').innerText = totalCuYards.toFixed(2); document.getElementById('resFeet').innerText = totalCuFt.toFixed(2); document.getElementById('resBags').innerText = bagsNeeded; document.getElementById('concreteResults').style.display = 'block'; }

---

How to Calculate Concrete Volume

Whether you are pouring a new backyard patio, a driveway, or setting fence posts, accurately estimating the amount of concrete you need is the difference between a successful project and an expensive emergency trip to the hardware store.

The Math Behind the Calculation

Concrete is measured in cubic yards. To calculate the volume for a standard rectangular slab, you follow these steps:

1. Convert all measurements to feet. (Example: 4 inches = 0.33 feet).
2. Multiply Length × Width × Thickness to get the Cubic Feet.
3. Divide the total Cubic Feet by 27 to get Cubic Yards.

Realistic Example: A 10′ x 10′ Patio

Imagine you are pouring a patio that is 10 feet long, 10 feet wide, and 4 inches thick:

• Calculation: 10 ft × 10 ft × 0.333 ft (4″) = 33.33 Cubic Feet.
• In Yards: 33.33 / 27 = 1.23 Cubic Yards.
• Using 80lb Bags: Since one 80lb bag covers 0.6 cu ft, you would need roughly 56 bags (without accounting for waste).

Why Add a Waste Factor?

We recommend adding at least 10% for "wastage." This accounts for several factors:

• Spillage: Small amounts lost during mixing and pouring.
• Form Deflection: The weight of the concrete can cause wooden forms to bulge slightly.
• Uneven Subgrade: If your dirt base isn't perfectly flat, some areas will be deeper than 4 inches, consuming more material.

Choosing the Right Bag Size

Concrete pre-mix bags typically come in three sizes. Their yield (how much space they fill) is standard across most brands like Quikrete or Sakrete:

Bag Weight	Yield (Cubic Feet)
80 lb (Standard)	0.60 cu ft
60 lb (Medium)	0.45 cu ft
40 lb (Light)	0.30 cu ft

Expert Tip: Bagged vs. Ready-Mix

If your project requires more than 1 cubic yard (roughly 45-50 bags of 80lb concrete), you should consider ordering a Ready-Mix truck. Mixing 50 bags by hand is physically exhausting and often leads to "cold joints," where one section starts drying before the next is poured, potentially causing cracks.