Short answer
To find the area of an L-shaped or irregular room, split it into rectangles and triangles and add the parts, or take the bounding rectangle and subtract the missing piece. A 6 m by 4 m room with a 2 m by 2 m corner missing is 20 m2 either way.
1. Method 1: add the parts
- 1Sketch the room and mark every wall length.
- 2Split it into rectangles (and triangles for angled walls).
- 3Find each area and add them.
Example: 6 × 2 + 4 × 2 = 12 + 8 = 20 m².
2. Method 2: subtract the missing part
Area of the bounding rectangle minus the missing corner: 6 × 4 − 2 × 2 = 24 − 4 = 20 m².
3. Method 3: coordinates
Write each corner as x, y and enter them in order under Irregular polygon in the Area Calculator. It uses the Shoelace formula.
4. Perimeter
With a notch in one corner the perimeter equals the bounding rectangle: 2(6 + 4) = 20 m. Notches elsewhere add length, so add up every wall.
5. Tips
- Use one unit for every length.
- Check that the parts add up to the same area by both methods.
For flooring and paint, see the Square Footage Calculator.
6. Frequently asked questions
How do I find the area of an L-shaped room?expand_more
Split it into two rectangles and add them, or subtract the missing corner from the bounding rectangle.
Does the perimeter change with a notch?expand_more
A notch in a corner leaves it unchanged. A notch in the middle of a wall adds its extra sides.
Can I enter an irregular shape directly?expand_more
Yes. Use Irregular polygon and list the corner coordinates in order.
What units should I use?expand_more
Any length unit, but use the same one throughout.