How it is calculated
Square footage of a rectangular room is length × width in feet. An L-shaped room is the main rectangle plus the extension. A triangle is half the base × height; a circle is π × diameter² ÷ 4. Wall area is the perimeter × 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 15 × 12 ft room is 180 sq ft with a 54 ft perimeter; with 8 ft ceilings the walls are 432 sq ft and the volume 1,440 cu ft.
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 calculate square footage?
Multiply length by width in feet: a 15 × 12 ft room is 180 sq ft.
How do I find the square footage of an L-shaped room?
Split it into two rectangles, find each area and add them.
How many square feet is a 12 × 12 room?
144 square feet.
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