How much paint do I need? Our Paint Calculator is a useful feature that calculates the amount of paint we require for a painting project. We will also soon be adding a feature that will allow you to calculate labour cost for the painting project. Usually for a 3 bedroom unit/house it takes 20L of ceiling paint. In most cases it's flat (for bathroom ceilings it's best to use mould proof or simple low sheen paint, 30 liters for walls usually its low sheen, and 4-6 Litres for woodwork.) Coverage in most cases is around 1L per 7 -10 Square meters, again it's for previously painted surfaces only. For new plasterboard its around 7 squares per 1 L per one coat, and the new render is 5 square meters per liter again for one coat.