Concrete calculator
Find out how much concrete you need for a slab, round column, or rectangular footing. Add a waste allowance and compare bag sizes.
Project details
How the volume is calculated
For a slab or rectangular footing, multiply length × width × thickness or depth. For a round column, multiply π × (diameter ÷ 2)² × height. Multiply by the number of identical shapes, then add your chosen waste percentage. All lengths are converted to matching units first. We use 3.141592653589793 as an approximation of π.
From volume to bags
One cubic yard equals 27 cubic feet. Divide the volume in cubic feet by the yield of a bag, then round up to a whole bag. This calculator uses 0.45 ft³ for a 60 lb bag and 0.60 ft³ for an 80 lb bag; your chosen product may differ.
These figures are the published approximate yields for QUIKRETE Concrete Mix No. 1101. Other products may differ. Check the yield printed on your bag before buying.
What can I estimate?
Slabs
Rectangular patios, paths, and pads with a uniform thickness.
Round columns
Solid cylinders with a constant diameter and height.
Rectangular footings
Straight rectangular sections with a uniform width and depth.
Measure more than once, allow for uneven ground, and check the yield on your bag or with your supplier. The two bag counts are alternatives—you do not need both.