Concrete Mix Calculator

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Concrete Mix & Volume Calculator

Results:

Total Volume: 0 Cubic Yards

Total Volume: 0 Cubic Feet

Estimated 80lb Bags: 0 bags

Estimated 60lb Bags: 0 bags

Estimated 40lb Bags: 0 bags

How to Calculate Concrete for Your Project

Planning a concrete project, whether it's a new driveway, a backyard patio, or footings for a deck, requires precise measurements. Ordering too little concrete leads to cold joints and structural weaknesses, while ordering too much results in wasted money and disposal headaches.

The Concrete Calculation Formula

Concrete is typically sold and calculated by the cubic yard. To find the volume of a rectangular slab, you use the following physical dimensions:

  • Volume in Cubic Feet = Length (ft) × Width (ft) × Thickness (converted to ft)
  • Volume in Cubic Yards = Total Cubic Feet ÷ 27

Note: Since thickness is usually measured in inches, you must divide the inch value by 12 to convert it to feet before multiplying.

Accounting for Waste

Professional contractors always add a waste factor of 5% to 10%. This accounts for variations in the subgrade (ground that isn't perfectly level), spillage, and concrete left in the mixer or pump line.

Understanding Bagged Concrete Yield

If you are mixing concrete yourself using bags from a hardware store, here is what you can expect per bag:

  • 80lb Bag: Yields approximately 0.60 cubic feet.
  • 60lb Bag: Yields approximately 0.45 cubic feet.
  • 40lb Bag: Yields approximately 0.30 cubic feet.

Example Calculation

Imagine you are pouring a patio that is 12 feet long, 10 feet wide, and 4 inches thick.

  1. Convert thickness: 4 inches ÷ 12 = 0.333 feet.
  2. Calculate cubic feet: 12 × 10 × 0.333 = 39.96 cubic feet.
  3. Convert to yards: 39.96 ÷ 27 = 1.48 cubic yards.
  4. Add 10% waste: 1.48 × 1.10 = 1.63 cubic yards.
function calculateConcreteVolume() { var length = parseFloat(document.getElementById('concrete_length').value); var width = parseFloat(document.getElementById('concrete_width').value); var thicknessIn = parseFloat(document.getElementById('concrete_thickness').value); var wastePercent = parseFloat(document.getElementById('concrete_waste').value); if (isNaN(length) || isNaN(width) || isNaN(thicknessIn) || length <= 0 || width <= 0 || thicknessIn <= 0) { alert("Please enter valid positive numbers for length, width, and thickness."); return; } // Convert thickness to feet var thicknessFt = thicknessIn / 12; // Base volume in cubic feet var cubicFeet = length * width * thicknessFt; // Apply waste margin var wasteMultiplier = 1 + (wastePercent / 100); var totalCubicFeet = cubicFeet * wasteMultiplier; // Convert to cubic yards var totalCubicYards = totalCubicFeet / 27; // Calculate bag counts // 80lb bag = 0.6 cubic ft // 60lb bag = 0.45 cubic ft // 40lb bag = 0.3 cubic ft var bags80 = Math.ceil(totalCubicFeet / 0.6); var bags60 = Math.ceil(totalCubicFeet / 0.45); var bags40 = Math.ceil(totalCubicFeet / 0.3); // Display results document.getElementById('res_cubic_yards').innerText = totalCubicYards.toFixed(2); document.getElementById('res_cubic_feet').innerText = totalCubicFeet.toFixed(2); document.getElementById('res_bags_80').innerText = bags80.toLocaleString(); document.getElementById('res_bags_60').innerText = bags60.toLocaleString(); document.getElementById('res_bags_40').innerText = bags40.toLocaleString(); document.getElementById('concrete_result').style.display = 'block'; }

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