How much paint do I need?

Coverage figures on tins assume a smooth, sealed, similarly-coloured surface. Bare plaster, textured walls and strong colour changes all use more, which is why people run out. The arithmetic is simple; the adjustments are what people miss.

What you'll need

• Tape measure
• Calculator (optional)
• Paint tin coverage figure (optional)

Step by step

1. Measure the height and width of each wall and multiply.Height times width per wall, added together. Work in metres to match the tin.
2. Deduct only large openings.Big windows and doorways, yes. Ignore small windows — the extra is useful slack rather than waste.
3. Read the coverage figure on the tin.Usually 10-14 m² per litre. It varies significantly by paint type, and matt covers differently from silk.
4. Divide the area by coverage, then multiply by the number of coats.Two coats is the realistic default. One coat is only enough over a very similar colour on a sealed surface.
5. Add extra for bare plaster or new surfaces.New plaster absorbs heavily and needs a mist coat — watered-down emulsion — first. Budget for that as an additional coat.
6. Add extra for textured or previously unpainted surfaces.Textured wallpaper, artex and bare wood use noticeably more than the stated figure.
7. Add extra coats for a big colour change.Dark to light needs three coats, or two over a tinted primer. Strong reds and yellows cover poorly regardless of direction.
8. Add about 10% and buy it all in one batch.Colour varies slightly between batches. Running out mid-wall and buying more later can show as a visible difference.

Tips

• Keep the batch number and a small labelled jar of leftover paint for touch-ups. It saves repainting a whole wall to fix one scuff.
• Ceilings usually need less than walls per square metre but are harder to apply evenly — buy generously.
• Cheap paint covers less, so it often costs more overall once you have used three coats instead of two.

Common mistakes

• Assuming one coat — Almost nothing covers properly in one coat. Budgeting for one is the standard reason for a second trip to the shop.
• Buying in separate batches — Batch-to-batch colour variation is real and shows as a visible band on a large wall.
• Ignoring the surface — Bare plaster and textured surfaces can use half again as much as the tin's figure suggests.

Questions people ask