Subtract a recess from a bounding rectangle, or add non-overlapping rectangles; both must produce the same area.
Method A: rectangle minus recess
Imagine a room inside a 4 × 3 m outer rectangle, but with a 1 × 1 m recess removed. The outer rectangle covers 4 × 3 = 12 m², the recess covers 1 m², and the actual floor area is 11 m².
This method is accurate when the missing corner is rectangular and both dimensions are known. Curved or angled walls require a more detailed outline.
Method B: sum rectangles
Divide the L into two non-overlapping rectangles. One area is 3 × 3 = 9 m², the other 1 × 2 = 2 m². Their total is again 11 m². The two methods should agree.
Record the outline
Number the vertices in perimeter order, moving consistently clockwise or counterclockwise. Do not draw intersecting sides: a self-intersecting polygon cannot represent one simple floor area.
Estimate tiles afterwards
Divide net area by tile area and add a cutting allowance. L-shaped rooms often create extra edge cuts, so a fixed allowance is a starting assumption rather than a guarantee.
Double-check
Measure walls in more than one place if they are not perfectly square, and verify especially tight dimensions before buying costly materials.
PisoExacto lets you start with an L-shaped plan and drag the vertices to match your room.
Try it in PisoExacto
Enter your own measurements and compare the result. Actual quantities depend on your materials.