L-shaped room area calculator
Measure the overall length and width, then the missing corner, to get the real floor area and perimeter.
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How to use it
- Enter overall length, overall width, cut-out length, cut-out width and unit.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Area = (overall length × overall width) − (cut-out length × cut-out width). The perimeter of an L shape with a square corner cut equals the full rectangle's: 2 × (length + width).
Example
Inputs: Overall length = 6, Overall width = 5, Cut-out length = 2, Cut-out width = 2, Unit = Meters. Result: Area: 26 m²; Area in square feet: 279.86 ft²; Cut-out area: 4 m².
Limits and caveats
- Assumes all corners are right angles and the cut-out is a rectangle.
- For more complex shapes, split them into rectangles and add the areas.
Questions about this tool
How do I measure the cut-out?
Picture the room as a full rectangle, then measure the length and width of the missing part at the corner.
Why is the perimeter the same as the rectangle's?
The two inner edges of the cut-out exactly replace the two pieces removed from the outer edges.
Can I split the room into two rectangles instead?
Yes, and you get the same result. Subtracting is usually easier because it needs fewer measurements.