Orpheus

How Much Paint Do I Need?

Litres and tins for a room, coats included.

Inputs
m
m
m

Each counted as 1.8 m².

Each counted as 1.5 m².

Coats
Include the ceiling
Paint needed
5.67 litres
Paintable area
31.2 m²
Wall area before openings
36 m²
Deducted for doors and windows
4.8 m²
Tins to buy
1 × 5 L + 1 × 1 L
Per coat
2.84 litres
litres = (wall area − openings) × coats ÷ coverage

Based on 11 m² per litre per coat, the usual figure for emulsion on a sealed surface. Bare plaster, new filler and a strong colour change absorb considerably more — allow an extra coat or a mist coat rather than trusting the first number.

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Multiply the room perimeter by the wall height, subtract doors and windows, multiply by the number of coats and divide by about 11 square metres per litre. A 4 by 3.5 metre room at 2.4 metres high needs roughly 6 litres for two coats.

How to use Paint Calculator

  1. Measure the room. Length, width and wall height in metres.
  2. Count openings. Doors and windows are deducted at standard sizes.
  3. Choose coats. Two is normal; a strong colour change usually needs three.
  4. Read litres and tins. The tin figure rounds up to what you can actually buy.

About estimating how much paint a room needs

Estimating paint is straightforward geometry with one variable that is not: how thirsty the surface is. The area itself is the perimeter of the room multiplied by the wall height, less the doors and windows, multiplied by the number of coats. Divide by the coverage figure on the tin and you have your litres. The figure on the tin assumes a sealed, previously painted surface in good condition, and that assumption is where estimates go wrong. Bare plaster absorbs dramatically more, which is why a mist coat — emulsion thinned with roughly ten percent water — exists at all. It soaks into the surface and seals it, and skipping it is a common reason new paint peels away in sheets months later. Fresh filler behaves the same way in patches, which is why a repaired wall often shows the repairs through the first coat. Colour matters as much as surface. Covering a dark shade with a light one, or painting over a strong red or yellow, routinely needs three coats regardless of what the tin promises, and a tinted primer will do it faster than another coat of the finish. The practical advice is to over-buy slightly and keep the receipt. Deducting openings generously and rounding down produces the one outcome worth avoiding: a second tin from a different batch, which can differ enough in shade to be visible on a large wall.

Frequently asked questions

How much area does a litre of paint cover?
Around 11 square metres per coat for emulsion on a sealed surface, though manufacturers quote between 10 and 14. Bare plaster, filler and freshly skimmed walls absorb far more, sometimes half again as much on the first coat.
Do I really need two coats?
Almost always. One coat over the same colour can work, but any change of shade shows through, and paint applied thinly to stretch a single coat wears unevenly. Two thin coats give a better finish than one thick one.
Should I subtract doors and windows?
Yes, but do not be too precise about it. Standard deductions of 1.8 square metres per door and 1.5 per window are close enough, and the small over-estimate that remains is useful — running out mid-wall is far worse than having some left.
What is a mist coat?
Paint thinned with about 10% water, applied to bare plaster so it soaks in and seals the surface. Without it, full-strength emulsion sits on top and can peel away later. It is not optional on new plaster, and it is why fresh walls need more paint than the calculation suggests.
Does the calculation cover ceilings?
There is a toggle for it, which adds the floor area to the total. Ceilings usually take a different paint, so buy them separately even though the area calculation is the same.

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