Enter length, width, and thickness — a 4-inch slab is standard for patios and sheds.
A 4-inch slab suits patios and shed floors; driveways and load-bearing pads usually want 5–6 inches. This view defaults to 4 inches — set your thickness first, then order 5–10% over for an uneven subgrade.
Why order extra? The headline number is the exact material your project needs. When you actually order, add about 5–10% on top — the “with 5% waste” figure in the result is a safe starting point. That margin covers what you lose to compaction, cuts around edges and corners, and ordinary spillage during handling. It is cheaper to have a little left over than to stop mid-job and wait on a second delivery.