Concrete Calculator
This free concrete calculator works out exactly how much concrete you need for any slab, footing, or pad. Enter your length, width, and thickness to get the volume in cubic yards and cubic feet, plus the number of 60 lb and 80 lb bags. With a built-in waste allowance, it helps you order the right amount of ready-mix or bagged concrete every time.
How to Use the Concrete Calculator
Enter the length and width of your slab in feet and the thickness in inches, then add how many slabs you are pouring. The calculator shows the volume in cubic yards and cubic feet, plus how many 60 lb and 80 lb bags you would need. Add a waste allowance so you do not run short on the pour.
How Concrete Is Measured
Ready-mix concrete is ordered by the cubic yard, while bagged concrete is measured in cubic feet. One cubic yard equals 27 cubic feet. For anything larger than a small slab, ordering ready-mix by the yard is usually cheaper and easier than mixing dozens of bags by hand.
Frequently Asked Questions
How do I calculate concrete in cubic yards?
Multiply length by width by thickness in feet, then divide by 27. The calculator does this automatically and shows the result in cubic yards.
How many bags of concrete do I need?
It depends on bag size. An 80 lb bag yields about 0.6 cubic feet and a 60 lb bag about 0.45. The calculator shows both counts for your volume.
Should I add extra for waste?
Yes. A 5–10% allowance covers spillage and uneven ground so you do not stop the pour short. The waste option adds this for you.
Is ready-mix or bagged concrete better?
For large pours, ready-mix by the cubic yard is usually cheaper and faster. Bags suit small jobs like post holes or a small pad.