Measure every wall and floor in metres, multiply length by width (or height) to get square metres, take off what you won't cover, then add a margin for waste. For paint that margin is the second coat. For flooring it's usually 10%. For tiles it's 10% on a simple job and more if there are lots of cuts. Get the measuring right and the shopping list falls out of it.
Kit and habits
A 5m or 8m tape, a pencil and a sketch of the room on paper are all you need. Draw the room as you see it from above, write each measurement on the drawing as you take it, and measure twice. Work in metres to two decimal places (2.35m, not 235cm), because that's how paint coverage, flooring packs and tile boxes are labelled.
Walls are rarely perfectly square. Measure at a couple of heights or points and use the larger figure.
Measuring walls for paint
The quick way is to measure all the way round the room at skirting height, then multiply by the wall height:
For a plain rectangular room that's 2 × (length + width) × height. Then take off the bits you won't paint. A standard internal door is about 1.5m², and the site's paint calculator uses that figure. Measure windows properly (width × height), as they vary far more than doors.
Don't bother deducting a light switch or a small vent. Do deduct anything that's going to be tiled, such as a splashback.
Awkward walls
- Chimney breasts and alcoves. Run your tape into the alcove and out round the breast rather than straight across. In a 4.2m × 3.6m room with a breast sticking out 0.4m, the distance round goes from 15.6m to 16.4m, because you add the two sides of the breast.
- Gable or sloping walls. Split them into a rectangle plus a triangle. A triangle is half the base times the height, so a triangle 3.6m wide and 1.2m tall is 2.16m².
- Stairwells. Treat each wall as its own shape and add them up. These are where people most often underbuy.
Paint: coverage and coats
Most standard matt and silk emulsions cover somewhere between 10 and 13m² per litre on smooth, previously painted plaster. We use 12m² per litre as a starting point, but the figure on the tin wins every time.
Two coats is normal. Allow a third if you're going light over a strong colour. New plaster soaks up the first coat (a mist coat of thinned emulsion), so expect that coat to go much less far, around 8 to 9m² per litre. One-coat paints are thicker and often cover only 8 to 10m² per litre.
Measuring a floor
Measure wall to wall at the widest points, into door openings and bay windows. For an L-shaped room, split it into two rectangles that don't overlap and add them together. A 4m × 3m room with a 2m × 1.5m extension is 12 + 3 = 15m².
Laminate, wood and click vinyl are sold in packs that cover a set number of square metres. Add a waste allowance, divide by the pack size and round up:
| Job | Flooring waste | Tile waste |
|---|---|---|
| Simple room, straight lay | 5 to 10% | 10% |
| Alcoves, bays, lots of doorways or pipes | 10 to 12% | 12 to 15% |
| Diagonal lay | 15% | 15 to 20% |
| Herringbone or chevron | 15 to 20% | 15 to 20% |
Measuring for tiles
Tiles work the same way, with one extra step: the grout joint. Each tile covers its own size plus a share of the gap, so a 100 × 200mm tile with a 2mm joint covers 102 × 202mm. On small tiles that makes a noticeable difference to the count.
One room, three ways
Take a kitchen 3.6m long and 3m wide with 2.4m walls. It has one door, one window of 1.2m × 1m, and a tiled splashback 3m long and 0.6m high.
Paint for the walls
- Distance round: 2 × (3.6 + 3) = 13.2m
- Wall area: 13.2 × 2.4 = 31.68m²
- Take off the door (1.5m²), window (1.2m²) and splashback (1.8m²): 31.68 − 4.5 = 27.18m²
- Two coats at 12m² per litre: 27.18 × 2 ÷ 12 = 4.53 litres
That's one 5 litre tin. Add the 10.8m² ceiling in the same paint and it goes up to 6.33 litres, so a 5 litre and a 2.5 litre.
Flooring
- Floor area: 3.6 × 3 = 10.8m²
- Add 10% waste: 11.88m²
- Packs of 2.2m²: 11.88 ÷ 2.2 = 5.4, rounded up to 6 packs (13.2m²)
Most people don't lay flooring under fitted units, so if the units cover a good chunk of the floor you can measure to the plinths instead.
Tiles for the splashback
- Area: 3 × 0.6 = 1.8m²
- Each 100 × 200mm metro tile with a 2mm joint covers 0.020604m²
- 1.8 ÷ 0.020604 = 87.4 tiles
- Add 10% waste: 96.1, rounded up to 97 tiles
Before you buy
- Check the batch or shade number on every box of tiles and every tin of coloured paint. Batches can differ slightly.
- Keep a few spare tiles and a spare pack of flooring. Matching them in a few years can be impossible.
- Compare price per litre. Two 2.5 litre tins often cost more than one 5 litre tin.
Plug your own measurements into the paint calculator, flooring calculator and tile calculator. They use the same sums as this guide.
Last reviewed October 2026.