Concrete Calculator: Cubic Yards and Bags for a Slab or Footing

How to do it

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   Step 1: Open Concrete Calculator: Cubic Yards and Bags for a Slab or Footing and add your input

   Type your numbers or text, add your file, or pick the options you need. Nothing is uploaded: everything stays in your browser.

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   Step 2: What Concrete Calculator: Cubic Yards and Bags for a Slab or Footing does

   Work out the cubic yards of concrete, ready-mix order and number of bags for a slab or footing.

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   Step 3: Read the result and compare

   The result appears at once. Change one value to see how the answer moves, then keep the figure that fits your case.

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   Step 4: Copy or save it

   Copy the result or download it. For an important decision, confirm it with the official source or an adviser.

About this tool

Enter the length, width and thickness in feet and inches, how many identical pieces you are pouring and a waste allowance. The calculator gives the volume in cubic feet and cubic yards, the order with waste, the number of 80 lb and 60 lb bags and the cost at your price per yard.

Formula

Volume in cubic feet = length × width × thickness in feet. Divide by 27 for cubic yards. Add 5% to 10% for waste, uneven ground and spillage.

Bags

An 80 lb bag of concrete mix makes about 0.6 cubic feet and a 60 lb bag 0.45 cubic feet. A cubic yard needs about 45 bags of 80 lb. Ready-mix trucks are priced by the yard and often have a minimum load.

Tips

For a footing enter its length, width and depth. For a round column use the volume of a cylinder instead. Order a little extra rather than run short: a cold joint weakens the slab.

Worked example

A 20 × 12 ft slab 4 inches thick is 80 ft³ or 2.96 yd³. With 10% waste you need 3.26 yd³, so order 3.5 yd³, or about 147 bags of 80 lb. At $165 a yard that is about $538.

Tips for best results

Check every box before you rely on a result, because one wrong digit changes the whole answer. Use the exact figures from your payslip, bill, certificate or contract, and keep a note of the date you calculated. Rates, thresholds and rules change from time to time, so for tax, fees and legal matters treat the output as an estimate and confirm with the official source named on this page. You can run as many scenarios as you like; nothing is saved or sent, and refreshing the page clears the boxes.