How to measure a room and work out how much flooring or tile to buy

Measure the room

1. Measure every wall at floor level, and write the lengths on a sketch of the room.
2. Measure the ceiling height. Check it in two places, because old floors and ceilings are rarely level.
3. Measure each door and window: width, height, and for windows the height of the sill above the floor.
4. Check that opposite walls agree. If they differ by a few centimetres, the room is not square: note both lengths.

Work out the floor area

For a rectangular room, multiply length by width. For an L-shaped or irregular room, split it into rectangles, work out each area and add them together.

For wall tiles or paint, multiply the length of each wall by the height you will cover, then subtract the area of the doors and windows that fall inside that height.

Add waste and round up to whole boxes

Cuts, breakage and mistakes mean you need more than the exact area. A common allowance is about 10% for tiles or planks laid in straight rows, and more for diagonal or herringbone patterns or small, awkward rooms. Your supplier can advise for your product.

Tiles and planks are sold in boxes covering a fixed area, so divide the area with waste by the area of one box and round up to a whole number. Keep a spare box or a few pieces for later repairs, since a later batch can differ in shade.

Let DecorHome do the arithmetic

In DecorHome you build the model once, with real wall lengths, doors and windows, then choose a material for each floor and wall. The materials list works out the area of each surface, subtracts the openings, adds a waste allowance set for each material, rounds to whole boxes where the material is sold in boxes and gives a price estimate.

Because models from sketches and plans are approximations, the estimate is shown as a range that depends on the precision label of the model. You can export the list, and paid plans can download it as a PDF to take to the shop.