There are 27 cubic feet in one cubic yard. Convert thickness to feet before multiplying and divide only the completed cubic-foot volume by 27.
Keep every dimension in compatible units
Length and width are commonly measured in feet while slab thickness is specified in inches. Divide inches by 12 first. A four-inch slab is one-third of a foot, not 0.4 feet.
Multiply length, width, and thickness in feet to get cubic feet. Divide that total by 27 to obtain cubic yards.
Calculate irregular work in pieces
Divide L-shapes into rectangles and calculate each separately. Treat footings, piers, steps, and thickened edges as additional volumes. Subtract only true voids that will not receive concrete.
Conversion is not the order decision
After calculating geometric volume, verify forms and subgrade, choose a reasoned allowance, and ask the ready-mix supplier about minimums and increments. The supplier and project specification determine the actual order.
Sources & further reading
References behind this guide
These sources support safety, measurement, or industry context. Product instructions, approved plans, and local requirements control your project.