16 October 2026Paint
How much paint do you really need?
Buy too little and the second batch never quite matches. Buy too much and buckets sit in the store for years. Here is the sum our counter uses.
From the Mainstay counter team
The short version
- Wall area: perimeter times height, minus doors and windows
- About 10 square metres per litre per coat
- Add 20 to 30 percent for new or rough walls
- Buy all of it from one batch
The basic sum
Add the length of all four walls and multiply by the height. That is the wall area in square metres. Take off about 2 square metres for each door and 1.5 for each window.
Most emulsions cover about 10 square metres per litre per coat. Two coats is normal. So a 4m by 3.5m room with 3m walls is 45 square metres, less a door and two windows, about 40 square metres. Two coats means 8 litres.
When to buy more
New plaster and fresh blockwork drink paint. Give them a thinned first coat and allow 30 percent more. Rough textured walls need 20 percent more. Strong colours over white may need a third coat.
Buy all your paint at once, from the same batch, and box it together before you start.
Buckets or tins
A 20 litre bucket is usually cheaper per litre than five 4 litre tins. Our project list picks the cheapest mix of buckets and tins for the litres you need.
Rainy season walls
Damp walls blister. Wait for two dry days before painting outside, and use an exterior weathercoat, not interior emulsion. Inside, open windows and run a fan so each coat dries in about two hours.