Paint Calculator: Litres for Walls and Ceilings

Measure the complete perimeter of the room along the skirting line with a steel tape, ensuring you follow alcoves, fitted cupboards, and chimney breast projections rather than taking a straight wall-to-wall measurement. Measure the vertical height from top of skirting to ceiling. Check the spreading rate on your paint tin; standard UK trade emulsion covers approximately 10 to 12 square metres per litre per coat.

Common mistakes when estimating paint quantities include:

• Skipping chimney breast side returns, deep door linings, and window reveals during perimeter measurements, resulting in unexpected paint shortages mid-job.
• Assuming a single coat will cover existing dark or vivid paint; transitioning from dark green or red to off-white invariably demands two to three full coats.
• Failing to account for the extreme porosity of bare, freshly skimmed plaster, which soaks up paint thirsty like a sponge unless sealed with a diluted mist coat first.

This estimator assumes smooth, pre-painted internal plaster walls in sound condition. It will underestimate paint volume on heavily textured surfaces such as Artex, rough masonry, blown wallpaper, or highly porous bare lime plaster, which can reduce coverage by 25% to 40%. For exterior masonry painting, specialist external coatings with significantly lower spread rates must be calculated according to manufacturer product sheets.

How the estimate works

Paintable area = perimeter × height − openings. Litres = area × coats ÷ 12 m² per litre.

Worked example (the default inputs)

A 16m perimeter at 2.4m high, minus 4 m² of openings, is 34.4 m². Two coats need about 5.7 litres: three 2.5L tins or two 5L tins.

Tips

• Buy all paint in one batch to avoid colour differences.
• Strong colour changes, especially going lighter, may need a third coat.
• Keep a small amount back for touch-ups and label the tin with the room.