Paint Calculator — How Much Paint Do I Need?
Free tool · Works offline · Rooms, walls & ceilings · Metric & imperial
How to calculate how much paint you need
Paint quantity is (paintable area × number of coats) ÷ coverage rate, plus 10% waste. The paintable area for a room is the total wall area minus doors and windows. A standard door is about 1.85 m² and a standard window about 1.4 m². Enter your room dimensions in the calculator and it deducts these automatically. Coverage rate varies by paint type — standard emulsion covers 10–12 m²/L on a smooth surface, less on new plaster or rough masonry.
How many litres of paint for a bedroom?
A typical 4×3.5m bedroom with 2.4m ceilings has about 32 m² of wall area (minus doors and windows ≈ 27 m² paintable). At 10 m²/L with 2 coats: 27 × 2 ÷ 10 = 5.4 litres. Buy two 3-litre tins. For the ceiling (4×3.5 = 14 m²): 14 × 2 ÷ 10 = 2.8 litres — one 3-litre tin. Total for the room: around 8–9 litres of emulsion for walls and ceiling combined.
How many coats of paint do you need?
This depends on the surface and colour change. 1 coat: touching up the same colour on a sound surface. 2 coats: standard for most repaints — gives even coverage and depth of colour. 3 coats: new plaster (which is very absorbent), dramatic colour changes from dark to light, or when using cheap paint with poor opacity. Always let each coat dry fully before applying the next — rushing leads to lifting and uneven finish. On new plaster, apply a mist coat first (emulsion diluted 20% with water) to seal the surface.
Paint coverage rates by type
Coverage rates vary significantly by paint type and surface. Standard vinyl emulsion: 10–12 m²/L on smooth surfaces. Gloss and satin: 8–10 m²/L. Masonry paint: 3–5 m²/L (rough surfaces absorb much more). Primer: 6–8 m²/L. Ceiling paint: 10–12 m²/L. On new or porous surfaces, coverage drops by 30–50% for the first coat. Always check the tin — manufacturers vary and the stated coverage is for smooth, sealed surfaces.
Tips to get a professional finish
Buy all tins from the same batch — colour can vary slightly between batches. Mix all tins together in a large bucket before starting. Cut in edges with a brush first, then roll the large areas while the cut-in is still wet (this prevents lap marks). Apply in good lighting — you'll see every missed patch. Two thin coats always beat one thick coat, which drips and takes longer to dry.
Frequently asked questions
How much paint for a 12×12 room?
A 12×12 ft (3.66×3.66m) room at 8ft (2.44m) ceiling height has about 35 m² of wall area. Minus 2 doors and 2 windows ≈ 30 m² paintable. At 10 m²/L with 2 coats: 6 litres. Buy two 4-litre tins.
How much paint for a ceiling?
Just multiply length × width. A 4×3.5m ceiling = 14 m². At 10 m²/L with 2 coats: 2.8 litres — one 3-litre tin is enough.
Do I need special paint for a bathroom?
Yes — use a paint with a sheen level of satin or semi-gloss, ideally one labelled "bathroom" or "kitchen & bathroom". These are more moisture-resistant and can be wiped down. Flat/matt emulsion will absorb moisture and develop mould patches.
How long does paint take to dry between coats?
Standard emulsion: 2–4 hours touch dry, 4–6 hours recoatable. Gloss and satins: 6–8 hours between coats. Oil-based paints: 12–24 hours. Temperature and humidity affect drying significantly — cold or humid conditions can double these times.