How it is calculated
The area of a rectangular room is its length times its width. An L-shaped room is the main rectangle plus the extension. A triangle is half the base times the height; a circle is π × diameter² ÷ 4. Wall area is the perimeter times the ceiling height, with no deduction for doors and windows.
Formula
Rectangle: A = L × WL-shape: A = L × W + a × b, perimeter = 2 × (L + W + b)Circle: A = π × D² ÷ 4Wall area = perimeter × HExample
A 5 × 4 m room is 20 m² with an 18 m perimeter; with a 2.6 m ceiling the walls are 46.8 m² and the volume 52 m³. Add a 2 × 1.5 m extension and the floor becomes 23 m².
Tips from practice
- Measure at floor level along the walls and round to the centimetre.
- Split an awkward room into rectangles and add them up.
- For laminate, tiles and paint use the matching calculator, which adds waste and pack sizes.
Questions and answers
How do I work out the area of a room?
Multiply the length by the width in metres: a 5 × 4 m room is 20 m².
How do I work out wall area?
Multiply the room's perimeter by the ceiling height.
How do I measure an L-shaped room?
As two rectangles added together: the main part and the extension.
Found a mistake in a formula? Write to [email protected]