Circular Slab Calculator
Round patio, fire pit, or equipment pad — same circle math. Pick the project, then enter the diameter.
This pad is about a cubic yard or more. A ready-mix truck is usually easier than mixing that many bags by hand.
How the numbers are figured
A round pad is a short cylinder: π × radius² × thickness. Radius is half the diameter. Thickness is converted from inches to feet. If you are pouring more than one identical pad, the total is that volume times the count. Divide cubic feet by 27 for cubic yards. Bags use the same US pre-mix yields as the rectangle slab calculator and round up.
Common questions
How do you calculate concrete for a circular slab?
Treat the pad as a short cylinder: pi times radius squared times thickness. Radius is half the diameter. Convert thickness from inches to feet, then divide cubic feet by 27 for cubic yards.
How many 80 lb bags for a 10 foot round slab?
A 10 foot diameter pad that is 4 inches thick takes about 26.2 cubic feet, or 44 bags of 80 lb mix, before waste. With 10% extra, plan on 48 bags.
Is a round patio the same math as a square slab?
No. A rectangle uses length times width. A circle uses the diameter. Pick this calculator for a round form and the slab calculator for a square or rectangle.