To work out how much paint you need, measure the area you are painting in square metres, multiply it by the number of coats, then divide by the coverage of your chosen finish. A typical bedroom of 4 by 3.5 metres needs around 5 litres of emulsion for two coats on the walls, and about 2.5 litres for the ceiling. The worked example below shows exactly how we get there.
Getting the quantity right matters more than it might seem. Every tin we sell is mixed to order, so it cannot be returned once tinted, and running short halfway through a wall means waiting for a second batch. A few minutes with a tape measure saves both.
Photo Credit: Farrow & Ball; Colour Used: Dimity (2008)
How to measure a room
- Add up the walls. Measure the length of each wall and add them together to get the perimeter. Multiply by the height from skirting to ceiling.
- Take off doors and windows. Measure each one (width times height) and subtract it. Farrow & Ball point out that their own calculator does not allow for windows, doors or alcoves, so this step is worth doing by hand.
- Multiply by the number of coats. All three brands we stock recommend two coats of topcoat.
- Divide by the coverage figure for your finish, listed below, and round up to the nearest tin size.
Coverage by finish
These are the brands' own figures, per litre for one coat. They are maximums on a smooth, sealed surface, so treat them as a best case.
- Farrow & Ball. Estate Emulsion 14 square metres; Modern Emulsion, Dead Flat, Flat Eggshell and Modern Eggshell 12; Casein Distemper 13; Exterior Masonry 8.
- Little Greene. Absolute Matt Emulsion 14 square metres; Intelligent Matt Emulsion approximately 14; Distemper approximately 15.
- Paint & Paper Library. Architects' Matt up to 14 square metres.
- Limewash is the exception. Little Greene give approximately 6 square metres per litre and four coats for full coverage, and Farrow & Ball say coverage varies with conditions. It needs a different calculation altogether.
Photo Credit: Little Greene; Colours Used: Pleat (280), Heat (24)
A worked example
Take a bedroom 4 metres long, 3.5 metres wide and 2.4 metres high, with one door and one window.
- Perimeter: 4 + 3.5 + 4 + 3.5 = 15 metres.
- Wall area: 15 × 2.4 = 36 square metres.
- Less the door (0.8 × 2.0 = 1.6) and window (1.2 × 1.4 = 1.68): about 32.7 square metres.
- Two coats: 32.7 × 2 = about 65.4 square metres of painting.
In Estate Emulsion or Absolute Matt Emulsion, at 14 square metres per litre, that is about 4.7 litres: one 5 litre tin. In Modern Emulsion, at 12 square metres per litre, it comes to about 5.5 litres, so a single 5 litre tin will fall a little short. Add a 2.5 litre tin, and keep what is left for touching up.
The ceiling is simpler: 4 × 3.5 = 14 square metres, or 28 for two coats. At 14 square metres per litre that is 2 litres, so one 2.5 litre tin.
For the woodwork, allow roughly 2 square metres for the skirting (about 14 metres at 15cm high), 1.6 for one face of the door and a little more for the frames: about 5 square metres, or 10 for two coats. At 12 square metres per litre that is a little under a litre of eggshell.
When you will need more
- New or porous plaster. Bare plaster drinks paint. It needs a primer or a thinned first coat, as each brand's instructions explain, and the topcoat will not go as far on the first pass.
- A big colour change. Farrow & Ball note that additional coats may be needed depending on the surface and topcoat colour. Going from a deep colour to a pale one, a coat of primer in a light tone will save paint overall.
- Textured walls. Rough or heavily patched surfaces simply have more area than a tape measure suggests.
- Primer. If you are priming, add it separately: one coat of Farrow & Ball Wall & Ceiling Primer & Undercoat covers 12 square metres per litre, so the walls above would need about 2.7 litres.
Photo Credit: Paint & Paper Library; Colours Used: Stone I (201), Stone II (202), Stone V (205), Moleskin (218)
Questions we are often asked
Should I round up or down?
Up. A little left over is useful for touch-ups, and it is always from the same batch.
Does a sample pot help with quantities?
Not with quantities, but it does stop you buying 5 litres of the wrong colour. Order sample pots first, then order the full amount once you are sure.
Can I mix finishes in one order?
Yes. Walls, ceiling and woodwork are usually different finishes, and each colour can be ordered in any finish its brand makes.
