Square feet calculator
Square footage is length times width when both are in feet. A 12 × 10 ft room is 120 square feet, which is 11.15 square metres. For a circle, multiply π by the radius squared; for a triangle, half the base times the height.
How to calculate square feet
The mistake that ruins a square-footage figure is mixing units mid-measurement: taking a room as 12 feet 6 inches and entering 12.6 rather than 12.5. Six inches is half a foot, not six tenths, and the error compounds across both dimensions. Where a room is genuinely irregular, splitting it into rectangles and adding them is more accurate than trying to average, and it is also how a flooring supplier will quote it. Alcoves, bay windows and chimney breasts each want their own small rectangle.
Questions
Multiply length by width, both measured in feet. For 12 ft 6 in, use 12.5 rather than 12.6.
10.764. Going the other way, one square foot is 0.0929 square metres.
Split it into two rectangles, calculate each, and add them. That is also how a supplier will quote it.
For flooring, yes if the floor continues into them. For carpet, ask the fitter: some measure the largest rectangle instead.
Flooring, paint, rent per square foot, property listings and heating loads. Almost every material quote starts with it.