Guide
Estimating an L-shaped pour
An L is two rectangles that share a corner. The slab calculator can add those pieces on one ticket. The only easy mistake is counting the corner square twice.
Split the drawing, not the pour
Stand at the inside corner. One rectangle is the long run. The other is the remaining stub, measured from the inside corner out, not from the far end of the first run. If the long arm is 20 ft by 10 ft and the stub is 8 ft by 10 ft, the shared 10×10 corner belongs to only one of those rectangles.
A common split: 20×10 plus 8×10, if the 8 ft is the leftover beyond the 10 ft width of the first piece. Sketch the two boxes on the dirt or on paper before you type. If the areas overlap on the sketch, the yardage will be high.
Use Add this rectangle
Enter the first box, add it, clear the length and width, enter the second box. The ticket keeps a running total and a 10 percent extra for waste on the sum. Thickness should be the same on both pieces unless the pad actually steps. If it steps, use the true thickness on each piece. Do not average them “to be safe” unless you want extra yards on purpose.
Walks and broken shapes
A sidewalk that turns is the same idea. The sidewalk calculator does one straight run. A landing or a dogleg is a second rectangle on the slab tool. A circle is not an L. Use the round calculator for that piece and add the two yardages yourself.
This is how you keep the geometry honest. It is not a layout for joints, steel, or a permit. If the L wraps a house corner, check the fall on both legs so water does not sit in the inside corner.