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How much paint do I need for the ceiling?

A flat ceiling has exactly the same area as the floor. Multiply by two coats, divide by 7-10 m² per litre — and add extra if the ceiling slopes.

The flat ceiling: the floor area is the answer

A flat ceiling is the easiest surface in the house to calculate, because it is identical to the floor beneath it. If the room has 15.1 m² of floor, the ceiling has 15.1 m². There are no doors or windows to subtract, and no perimeter to measure.

The sum for a room measuring 4.20 × 3.60 m: 4.20 × 3.60 = 15.1 m². Two coats: 15.1 × 2 = 30.2 m² of painted surface. At 7 m² per litre: 30.2 ÷ 7 = 4.3 litres. At 10 m² per litre: 3.0 litres. Add 5-10 % for waste, and you land on 3-5 litres — one 5-litre tin, with some left over.

Ceiling paint typically goes further than wall paint, because ceilings are usually smooth and already painted. Matte ceiling paint is most often rated at 7-10 m² per litre per coat, and it is usually the cheapest paint per litre in the range. The figures on the tin itself always take priority over the numbers in an article.

The sloped ceiling: the area is larger than the floor

In a loft room or under a sloping roof, the ceiling surface is longer than the floor beneath it, because it slopes. Measure the floor and you get too small a number — and you will run short of paint at the end.

Instead measure along the slope, from the top of the knee wall up to the ridge, or to the flat section in the middle. A loft room with a 4.00 × 3.00 m floor, where the sloped sides measure 2.20 m along the incline on each side and there is a 0.80 m flat ceiling section in the middle: (2.20 + 0.80 + 2.20) × 4.00 = 5.20 × 4.00 = 20.8 m² of ceiling surface — against 12 m² of floor. That is 73 % more paint than the floor area would have suggested.

If you don't have a tape measure that can reach up there: on an ordinary pitched roof, the sloped surface is roughly 1.1 to 1.4 times as long as the horizontal distance it covers — flat towards the low end, steep towards the high end. Use that for an estimate, not for placing an order.

HouseSense works out the ceiling area itself once the room has been scanned with LiDAR or drawn in the app, and builds the sloped ceiling from the shape of the gables rather than assuming the ceiling is flat. If you're unsure how much sloped ceiling a loft room actually has, the drawing is faster than the ladder.

Why the ceiling gets painted first

The order is ceiling, then walls, then woodwork. Ceiling paint splatters — matte paint is thin and gets rolled overhead — and those splatters land on the walls. Paint the walls first, and you paint them twice.

That also means you don't need to be fussy about the line between ceiling and wall while painting the ceiling: roll calmly a couple of centimetres down the wall. The wall paint will cover it afterwards, and you avoid cutting a sharp edge twice.

When two coats aren't enough on the ceiling

The ceiling is the surface where a single coat most often gives itself away, because light falls along it and highlights every single roller stripe. Plan for a third coat in these cases:

• Water stains after a leak. They bleed through coat after coat. Use a blocking primer on the spot first — ordinary ceiling paint won't stop them.
• Nicotine, soot or smoke. Same problem, same solution: blocking primer over the whole surface, not just the stains.
• New plaster or freshly filled patches. Uneven absorption causes patchiness. Prime first.
• Wood ceiling to be painted white. Knots bleed through yellow; this needs a blocking primer and typically three coats.

Textured, boarded and beamed ceilings

A textured plastered ceiling, a felted surface, or a boarded ceiling has more surface area than its footprint, and the roller has to work harder to get the paint down into the texture. Add 10-20 % to your usage on a textured ceiling, and up to 30 % on tongue-and-groove boards, where every groove has to be filled.

Exposed beams are typically painted with wood paint and calculated separately: measure the beam's width plus its two sides, multiply by the length, and add it to the total. A beam 15 cm wide and 20 cm high over 4 metres gives (0.15 + 0.20 + 0.20) × 4 = 2.2 m² per beam.

The bathroom and kitchen ceiling

A bathroom ceiling is small — typically 4-6 m² — but it is the hardest-worked surface in the home. Steam condenses on the ceiling, and ordinary matte ceiling paint doesn't handle moisture or wiping down particularly well. Use a paint designed for wet rooms or high humidity, and expect it to cover less than ordinary ceiling paint: typically 6-9 m² per litre per coat against 7-10.

The kitchen ceiling has the same problem in a milder form: fumes and grease settle on it, and the ceiling needs to withstand a wipe with a cloth. Choose a ceiling paint with a bit of sheen rather than matte — matte paint turns glossy where it's wiped, and the mark can't be rubbed away again.

If the ceiling is already yellowed by fumes or nicotine, neither extra coats nor a pricier paint will help. It needs a blocking primer over the whole surface first, and then two coats on top — otherwise the discolouration bleeds through within a few months.

Quick guide in words: how many litres for the ceiling?

Two coats of matte ceiling paint, coverage calculated at 7-10 m² per litre, waste included:

• Bathroom, 5 m²: approx. 1-1.5 litres. Buy 2.5 litres.
• Bedroom, 12 m²: approx. 2.5-3.5 litres. Buy 5 litres.
• Living room, 25 m²: approx. 5-7.5 litres. Buy 10 litres.
• Whole flat, 80 m²: approx. 17-24 litres. Buy 2 × 10 litres plus a 5-litre tin.

Better to buy a little too much than a little too little. A leftover tin is useful for touch-ups two years from now; an extra trip to the shop midway through the second coat can mean the join between old and new tin shows — especially if the new one is a different batch of tint.