How Much Concrete Do I Need?
Use project length, width, and thickness to estimate concrete in cubic yards, then add a practical planning allowance before ordering.
Use the concrete calculator first
Enter the length and width in feet and the thickness in inches in the ATHENA Concrete Calculator. The calculator converts the dimensions to cubic yards and adds 10% to the recommended order quantity.
How to calculate concrete volume
For a rectangular slab, first convert thickness from inches to feet, multiply length × width × thickness, and then divide cubic feet by 27 to get cubic yards.
Cubic yards = length × width × thickness in feet ÷ 27
How much concrete do I need for a 30 × 10 ft area at 4 inches?
A 30 × 10 ft area at 4 inches is about 3.7 cubic yards. With ATHENA's 10% planning allowance, the recommended planning quantity is about 4.1 cubic yards.
What if the area is irregular?
Divide an irregular project into smaller rectangles or other manageable sections. Calculate the volume of each section separately, then add the results. This gives you a better estimate than treating an irregular shape as one oversized rectangle.
Why add a planning allowance?
The 10% allowance is intended to provide room for normal measuring, placement, and ordering variation. It is a planning estimate rather than a guarantee of the exact quantity required.
What about concrete bags?
For bagged concrete, compare the cubic-yard result with the yield printed on the product package. See the concrete bag planning guide or Concrete Bag Calculator for conversion examples.
Ready-mix or bagged concrete?
Use the cubic-yard quantity when discussing a ready-mix delivery with a supplier. For bagged mix, convert the volume using the exact product's yield and round up to whole bags.
Ready to calculate?
Enter your project measurements here: Free Concrete Calculator or see Concrete Calculator for a Slab.
Compare 80-lb concrete mix on Amazon (paid link)
Ordering note
For ready-mix deliveries, confirm the final cubic-yard order with your concrete supplier. For bagged mixes, use the exact product yield shown on the bag or product specification.
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