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How much paint do you need for a room or a house facade
Work out the wall and ceiling area, the number of coats and the coverage, add primer and a reserve, and you get the number of cans. Plus a note on POLUS RAL tinting and its minimum batch.
Calculate the wall and ceiling area
Wall area is the room perimeter multiplied by the height, minus windows and doors. For a 4 × 5 m room with a 2.7 m ceiling the 18 m perimeter gives 48.6 m²; subtract a window of about 2 m² and a door of about 1.6 m² and roughly 45 m² remains. The ceiling area equals the floor area, here 20 m². Niches, reveals and projections add a little; it is easier to put them into the reserve.
If only part of the walls is painted, say an accent wall, count just that. For a corridor or bathroom the formula is the same, but there are more openings, so the area turns out noticeably smaller than it looks.
Coverage and number of coats
On a smooth, filled wall a water-based emulsion covers roughly 8–10 m² per litre per coat; on textured plaster, paintable wallpaper or an unprimed surface noticeably less. The exact figure is on the can: the manufacturer states it for its own product. Walls are usually painted in two coats, and in three when going from a dark colour to a light one or with saturated shades.
For our room: walls 45 m² × 2 coats = 90 m²; at 9 m² per litre that is 10 L. Ceiling 20 m² × 2 = 40 m², another 4.5 L or so. Add a 10–15 % reserve for absorption, touch-ups and uneven spots: about 11 L for the walls and 5 L for the ceiling. Paint is often sold by weight: water-based paints have a density of roughly 1.4–1.5 kg per litre, so a 15 kg bucket is about 10 L.
Facades absorb more and use more paint
Facade area is counted the same way: house perimeter × wall height minus windows and doors, with gables added separately as triangles. Render, concrete and aerated block absorb more than smooth walls, and facade paint consumption can be about one and a half times higher than interior paint over the same area. Facades get an exterior paint, silicone or acrylic for example, again in two coats.
Example: a 10 × 8 m house with 3 m walls has a 36 m perimeter and 108 m² of wall, minus about 15 m² of openings, roughly 93 m². At 6–8 m² per litre and two coats you need around 25–30 L plus a reserve.
Primer before painting
A deep-penetrating primer evens out absorption, binds the filler and reduces paint consumption: often one coat of paint over primer gives what one and a half coats give without it. Primer goes roughly 5–10 m² per litre depending on how absorbent the base is; on facades and fresh render closer to the lower end. Paint on an unprimed wall can dry patchy, especially over filler.
If the wall was already painted and the coating is sound, washing it and priming only the filler patches is enough. Old chalk whitewash has to be removed: neither primer nor paint will hold on it.
POLUS and RAL tinting
POLUS is a Georgian paint factory; its wall and facade paints are tinted to RAL catalogue colours at the plant. The minimum batch per colour is 10 cans of up to 10 kg or 20 cans of 15–20 kg, with a tinting surcharge of 10 GEL per can up to 10 kg and 20 GEL per 15–20 kg can. So tinting is ordered for the whole volume at once: one batch is guaranteed to match, while buying more of the same batch later is not always possible.
For a small job it is simpler to buy a white base and a tinting colourant: the paste is mixed into the bucket thoroughly. Saturated and dark shades use base C. Keep one can for touch-ups after the renovation.
Quick reminder
Perimeter × height − openings = wall area; ceiling = floor area. Multiply by the number of coats (usually 2), divide by the coverage from the can (a guide of 8–10 m² per litre for interior walls, 6–8 for facades), add 10–15 %. Primer: 1 L per 5–10 m². For POLUS RAL tinting count in batches of 10 or 20 cans. An 18–25 cm roller for walls, a brush for corners and edges, masking tape and film are all at ASB Trade alongside the paint.
Frequently asked questions
How much paint for an 18 m² room?
With a 2.7 m ceiling the walls are about 40 m² after openings. Two coats at 9 m² per litre need about 9 L, 10 L with a reserve; the ceiling takes another 4 L or so.
Why did the paint dry patchy?
Most often the wall was not primed: filler absorbs unevenly. A deep-penetrating primer and one more coat of paint will fix it.
Can a single can of POLUS be tinted to RAL?
Not at the factory: the minimum batch is 10 cans of up to 10 kg or 20 cans of 15–20 kg. For a single can take a white base and a colourant.