Measure the walls, subtract the openings, multiply by coats, then buy tins that actually exist. A shop that tells you “4.2 litres” is not finished — you cannot take 0.2 L off the shelf.
Room and paint
Estimate
Litres to buy6.8L
Paint required
6.425 L
Net wall area
25.70 m²
Area × coats
51.40 m²
Tin mix
2 × 2.5 L + 2 × 0.9 L
Leftover in the tins
0.375 L
Estimate only. Porous plaster, dark colours, and new plasterboard drink more than the label. Stir the same batch across walls, and keep a touch-up tin from the same lot.
How the calculator works
Paint is sold in tins, not in theoretical litres. The calculator therefore does four things: it finds the wall area, subtracts openings, multiplies by the number of coats, and then packs the litres into tin sizes you can actually buy.
Wall area is the run times the height. A 12 m run at 2.40 m is 28.8 m². Doors and windows come off that number — you will still cut in around them, so do not subtract every square centimetre of architrave. A standard interior door is about 1.6 m²; a living-room window is often 1.2–1.8 m². The worked example subtracts 3.1 m² and leaves 25.7 m² of paint.
Two coats is the default because one coat of a new colour on old emulsion rarely hides. Coverage of 8 m² per litre is deliberately conservative. A tin that boasts 12 m²/L is quoting a thin coat on a sealed surface. New plaster, textured wallpaper you are painting over, and deep reds drink more.
The tin pack is the part most online calculators skip. 6.425 L is not a product. On a shelf of 10 L, 2.5 L, and 0.9 L tins — the sizes Tikkurila, Vivacolor, and the Bauhaus / K-Rauta aisles actually hold — the mix with the least leftover is two 2.5 L and two 0.9 L (6.8 L). A single 10 L tin “works” and wastes 3.6 L.
Why the tin mix matters
Leftover paint is not free insurance if it is the wrong size. A 10 L tin that you open for a 6 L job skins over, and you will not use the last third on the next room a year later. Smaller tins cost more per litre and keep better.
The search tries every sensible count of each size, keeps the combinations that cover the litres, and picks the one with the smallest leftover, then the fewest tins. You can type other sizes in the advanced panel if you found a 3 L or 1 L range.
Worked example
A typical living-room wall run in a panel flat, two coats, one door and one window.
12 m run, 2.40 m high
Gross wall area = 12 × 2.40 = 28.8 m².
Openings = 3.1 m² (door + window).
Net area = 25.7 m².
Film = 25.7 × 2 coats = 51.4 m².
Litres at 8 m²/L = 51.4 ÷ 8 = 6.425 L.
Best tins = 2 × 2.5 L + 2 × 0.9 L = 6.8 L (0.375 L leftover).
A 10 L tin would leave 3.575 L unused.
Questions people ask before they open a tin
How much paint do I need for a room in Estonia?
Add the wall widths, multiply by the ceiling height, subtract doors and windows, then multiply by coats and divide by 8 m² per litre unless the tin says otherwise. A 12 m run, 2.40 m high, 3.1 m² of openings, two coats is 6.425 L — buy the 6.8 L tin mix, not a single 10 L.
Should I subtract doors and windows?
Yes, unlike wallpaper. Paint is bought by the litre of film, and a door is a real hole. Subtract the glazed or slab area, not the whole wall that happens to contain a door.
Why is the default coverage only 8 m² per litre?
Manufacturer figures assume a sealed, smooth wall and a thin coat. Two reasonable coats on ordinary emulsion in a panel flat land closer to 7–9 m²/L of tin. You can type 10 or 12 if you are rolling a second coat of the same colour on good plaster.
What tin sizes are sold in Estonian DIY shops?
The common interior wall range is 0.9 L, 2.5 L, and 10 L. Some lines add 1 L or 3 L. Type whatever is on the shelf in the advanced field, comma-separated.
Is this enough paint for the ceiling too?
No. Use this calculator for the walls, then run it again for the ceiling: type the ceiling area as the wall run with height 1 m (so 20 m² becomes a 20 m run at 1 m high) and one or two coats.