Concrete Calculator
How many cubic yards & bags of concrete you need
Pouring a slab, footing, walkway or post holes? Enter your measurements to find out exactly how much concrete to order — in cubic yards for ready-mix, or as a count of 40, 60 and 80 lb bags.
How to calculate concrete
Concrete volume is length × width × thickness. Our calculator keeps the units consistent (converting inches to feet) and adds a waste factor (10% by default) because no pour is perfectly level.
Cubic yards vs. bags
- A 40 lb bag yields about 0.30 ft³
- A 60 lb bag yields about 0.45 ft³
- An 80 lb bag yields about 0.60 ft³
Over about half a cubic yard, ready-mix is usually cheaper than mixing by the bag.
Frequently asked questions
How many 80 lb bags of concrete are in a cubic yard?
About 45. One 80 lb bag yields roughly 0.60 cubic feet, and a cubic yard is 27 cubic feet (27 ÷ 0.60 ≈ 45).
How much extra concrete should I order?
Add about 10% for waste, spillage and uneven subgrade; 10–15% for large or critical pours.