From flat slabs to real shapes
What you'll learn
See why an irregular driveway is just area × thickness — and prove it in 3D.
Real jobs are rarely a clean rectangle. An L-shaped patio, a driveway that tapers, a path that bends — they all look harder than a slab. They aren't.
Area is the only thing that changes
Volume is always area × thickness. For a rectangle, area is length × width. For any straight-sided shape, the area still exists — you just compute it differently (the calculator uses the surveyor's formula over the corners).
The thickness term never changes. So once you know the area of your shape in square feet, the rest is identical to a plain slab.
See it for yourself
The shape below is extruded to a 4-inch slab. Its area is labeled on top. Drag to rotate it — notice the thickness is uniform everywhere, no matter how the outline bends. That uniform thickness is exactly why area is all you need.
Loading 3D viewer…
The takeaway
Don't let an odd outline intimidate the estimate. Find the area, multiply by thickness, divide by 27. The any-shape calculator does the area for you — now you know what it's doing under the hood.
Check your understanding
Question 1 of 1
For an L-shaped slab of uniform thickness, the volume is: