Room area calculator
Floor area is length times width. Wall area is the perimeter times the ceiling height, minus doors and windows. Volume is floor area times height. A 4.5 × 3.2 m room with 2.4 m ceilings has 14.4 m² of floor, 33.7 m² of wall after openings, and 34.6 m³ of air.
How to measure a room
The volume figure is the one people skip and then need. It sizes heating and cooling, it sets ventilation requirements, and it is what a dehumidifier or air conditioner is rated against. The perimeter matters too: it is the length of skirting, coving or beading you will buy, and it is the number for a wallpaper order. Measuring once and reading all four figures is the entire point of doing it in one place rather than four.
Questions
Length times width, both in the same unit. For an irregular room, split it into rectangles and add them.
A standard internal door is about 1.8 m² (0.76 × 2.0 m). A typical window is 1.2 to 1.5 m².
It sizes heating, cooling and ventilation. Air conditioners and dehumidifiers are rated by the volume of air they can handle.
At floor level for area, since that is what flooring covers. Walls can bow, so measure the widest point if the two differ.
Not always. Property listings sometimes exclude areas under a low sloping ceiling, so check the definition being used.