Concrete Calculator
Estimate cubic yards, waste allowance and approximate 80-lb bag count.
Project inputs
Enter your measurements. Results update automatically.
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See estimating toolsHow much concrete do I need?
Start with the slab or pad length and width in feet, then enter thickness in inches. The calculator converts thickness to feet, finds cubic feet, and divides by 27 to convert the result to cubic yards. Your waste allowance is then added to the order quantity.
Concrete formula
Length × width × thickness in feet ÷ 27 = cubic yards. For a 4-inch slab, thickness in feet is 4 ÷ 12. Add a waste allowance after calculating the basic volume.
Bag estimate
The 80-lb bag estimate assumes about 0.60 cubic feet of yield per bag. Actual yield varies by product, so check the bag label before buying.
What can change the amount?
Uneven subgrade, thickened edges, footings, grade beams, over-excavation and spills can increase the amount of concrete needed. Measure the actual project and confirm ready-mix order quantities with your supplier.
Common concrete calculator questions
How many cubic feet are in one cubic yard?
One cubic yard equals 27 cubic feet.
Should I order exactly the calculated amount?
Most jobs need some extra material for field conditions and waste. Use the editable waste allowance to match the project rather than relying on a fixed percentage.
Can I use this for footings?
You can calculate rectangular sections, but irregular shapes and multiple footing runs should be measured separately and added together.