Room Area Calculator

Length times width gives the floor, the perimeter times height gives the walls, and floor times height gives the volume. For a 4 × 5 m room with a 2.7 m ceiling that is 20 m², 48.6 m² and 54 m³ — and using the floor figure to buy paint is the mistake this page exists to prevent.

The volume matters for heating and ventilation, not for materials: a radiator is sized on cubic metres, wallpaper on wall square metres adjusted for openings, and flooring on floor square metres plus waste.

Split L-shaped rooms into two rectangles, measure each, and add. For a bay or an alcove, treat the recess as its own rectangle and add it. A sloped ceiling means the floor area is still the floor, but the wall area has a trapezoid that a rectangular calculation will overestimate.

Measure at several points rather than once. Rooms in older buildings are rarely parallel, and the difference between the widest and narrowest width can be 5 cm — 0.2 m² on a small room, and enough to throw a flooring order off by a pack.

Once the floor and wall areas are known, each material has its own rule: paint at 10 to 14 m² per litre per coat, laminate in packs with 5 % waste, tiles with 10 %, wallpaper by drops rather than area. The area is the input; the material rules are where the quantity actually comes from.

Compare the result with a bill of quantities if you have one. A discrepancy of more than 10 % usually means one of you counted a room twice, or one of you measured the floor where the material goes on the wall.