When painting a room, you want to avoid running out halfway through the job or opening more tins than necessary. The amount of paint depends on the surface area, product coverage, wall condition and number of coats. The coverage printed on the tin is a guide; real consumption can vary significantly from one wall to another.
Paint quantity formula
Litres = (area to paint ÷ coverage per litre) × number of coats. Subtract large windows and doors if they will not be painted. Rough, porous or dark surfaces may need more paint, while a suitable primer can affect the amount required.
Two examples
A room has 42 m² of wall area in total. Windows and doors account for 6 m², leaving 36 m². The paint covers 8 m² per litre and you plan two coats: 36 ÷ 8 × 2 = 9 litres. A small reserve is sensible, especially if you may need touch-ups later.
A single wall is 4.5 m wide and 2.5 m high, giving 11.25 m². At 10 m² coverage per litre and two coats, you need 11.25 ÷ 10 × 2 = 2.25 litres. The paint calculator helps compare different coverage rates.
When should you measure more carefully?
Calculate separate areas for multiple colours, feature walls, textured plaster or a change from a dark colour to a light one. Keep the product name, shade and batch number for future purchases. If the manufacturer recommends it, mix tins together before painting to reduce visible shade differences.
Common mistakes
- Measuring only one wall and guessing the rest.
- Forgetting the number of coats.
- Treating the stated coverage as a guarantee.
- Subtracting windows while forgetting that reveals may also need paint.
The technical data sheet for the exact product takes priority over any general estimate.
Additional practical tip
A sensible process is to measure the room, add the surfaces, subtract areas that will not be painted and only then apply the product coverage rate. Also read the instructions on drying time and recoating. Two thin, even coats may give a better finish than one very thick coat.
Read next: Related guide and calculator.
Product choice also affects indoor air quality. Germany’s Federal Environment Agency provides guidance on healthier, more sustainable renovation.
Consider the surface and colour
The same paint can cover two walls differently. Smooth, primed plaster generally absorbs less material than a rough or highly absorbent surface. A strong colour change may also require additional coats. Read the manufacturer’s technical information and check whether the stated coverage applies to one coat or more. If you are uncertain, test a small area first. This helps you assess opacity, colour appearance and actual consumption. Allow enough drying time and apply the next coat only when the product instructions say the surface can be recoated. Good preparation often saves more paint and time than making an overly tight purchase estimate.