How this calculator works
For rooms, each row is length by width. For walls, use width by height. Split irregular shapes into non-overlapping rectangles, and enter doors or windows as their combined area in the square of the selected unit.
The formula
Gross area = sum of each rectangle’s length × width. Net area = gross area − openings.A quick example
A 5 m × 4 m room and a 3 m × 2 m room total 26 m². Subtracting 2 m² of openings leaves 24 m².
How to use this calculator
- Choose the settings that match your scenario, using the units shown beside each field.
- Enter rooms or wall sections: length,width per line, total openings to subtract (selected unit²).
- Calculate, then review the method and assumptions alongside the results.
A few common questions
Can I mix rooms and wall sections?
The arithmetic works, but keep them in separate calculations if they represent different materials or surfaces.
What unit should I use for openings?
Use the square of the selected length unit: for feet enter ft², and for meters enter m².