Concrete Calculator
Estimate how much concrete you need — in cubic yards, cubic feet and premix bags — for a slab, footing or column.
Project shape
Concrete needed
Add ~10% for waste. Ready-mix is ordered by the cubic yard; 27 cubic feet = 1 yard.
Frequently asked questions
How much concrete do I need for a slab?
Multiply length × width × thickness to get the volume, then convert to cubic yards (divide cubic feet by 27). Add about 10% extra for spill and uneven ground.
How many 80 lb bags of concrete are in a yard?
Roughly 45 bags of 80 lb premix make one cubic yard (each 80 lb bag yields about 0.6 cubic feet). For 60 lb bags, it is about 60 per yard.
How thick should a concrete slab be?
A typical 4 inches works for patios and light foot-traffic slabs, 4–6 inches for driveways, and 6+ inches for heavy vehicles. Thicker is safer for weight-bearing surfaces.
What is a cubic yard of concrete?
A cubic yard is 3 × 3 × 3 = 27 cubic feet. Ready-mix concrete is usually ordered by the cubic yard, which is why most contractors think in yards.
Why add extra concrete over the calculated amount?
Ground is rarely perfectly level, forms can shift, and some concrete is wasted in spill and tools. A 10% overage is the standard safety margin for estimating.