L-Shaped Room Area Calculator
Find the floor area and perimeter of an L-shaped room by subtracting the missing corner from the full bounding rectangle.
How it works
Area = (overall length × overall width) − (cut-out length × cut-out width) · Perimeter = 2 × (overall length + overall width)
An L-shaped room is a full rectangle with one rectangular corner missing, so its area is the bounding rectangle minus that cut-out. Measuring the overall length and width plus the two sides of the missing corner is all you need. Interestingly, the wall perimeter of an L equals the perimeter of its bounding box, because the two edges that step inward add back exactly what the outer corner would have contributed.
Worked example
A room that is 20 × 15 ft overall with an 8 × 6 ft corner cut out has an area of 300 − 48 = 252 sq ft (about 23.4 m²), and a wall perimeter of 2 × (20 + 15) = 70 ft.
Frequently asked questions
How do I measure an L-shaped room?
Measure the overall length and width as if the room were a full rectangle, then measure the length and width of the missing corner. The calculator subtracts the corner from the whole.
Why is the perimeter the same as a rectangle?
When a corner is notched in, the two new inner edges together equal the horizontal and vertical lengths the removed outer corner would have had, so the total wall length is unchanged from the bounding rectangle.
Can I use this for flooring or paint quantities?
Yes — the floor area drives flooring, carpet and tile quantities. Add about 10% for waste and cuts, and use the perimeter for baseboard or trim.
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This calculator is for educational purposes. Double-check important results before acting on them.