How to estimate paint for a room

For a rectangular room, wall area is approximately 2 × (length + width) × height. That is the perimeter times the ceiling height. Measure in metres or feet consistently — mixing units is the usual source of wild answers.

Subtract doors and windows. If you do not want to measure each one, a typical interior door is around 2 m² and a typical window might be 1–2 m², but your house will differ. The calculator uses simple averages; override by measuring if the room is mostly glass.

Ceilings are a separate rectangle: length × width. Many people paint walls and ceiling with different products, so keep those quantities apart.

Coverage is on the tin — often about 10–14 m² per litre for emulsion, or roughly 300–400 ft² per gallon, depending on brand and surface. Rough plaster drinks more paint than a previously painted smooth wall.

Two coats are common on walls. Dark colours over light, or stain-blocking, can need more. Multiply area by coats, then divide by coverage per litre (or gallon) to get volume.

Round up to whole tins and add a little for touch-ups. Keeping a labelled leftover tin for later repairs is cheaper than trying to match a discontinued batch in two years.

Wallpaper is counted in drops and roll length, not litres — use the Wallpaper Calculator. Flooring and tiles use area plus wastage for cuts. Paint wastage is usually smaller unless you are spraying.

If you only have measurements in mixed units, convert with the Area or Length converters first, then enter one system into the paint tool.

These estimates assume a simple box room. Alcoves, stairwells, and textured surfaces need a site look. When in doubt, ask the merchant with your measurements in hand.