Short answer: one litre of ordinary wall paint covers about 10 m² per coat, and one US gallon about 350 ft². Most walls need two coats, so a 12 × 12 ft bedroom with 8 ft walls takes about 2 gallons (7.6 litres), and a 3 × 4 m room with 2.5 m walls about 6.3 litres.
The rest of this guide shows where those numbers come from, so you can check your own room.
The rule: wall area × coats ÷ coverage
- Measure the wall area. Add up the length of all the walls (the room's perimeter) and multiply by the wall height. A 12 × 12 ft room has 48 ft of wall; at 8 ft high that is 384 ft².
- Take off doors and windows. A standard door is about 20 ft² (1.9 m²), a window about 12–15 ft² (1.4 m²). Our example loses one of each: 384 − 20 − 12 = 352 ft².
- Multiply by the coats. Two coats: 704 ft².
- Divide by the coverage on the tin. At 350 ft² per gallon: 704 ÷ 350 = 2.0 gallons.
In metric it works the same way: 3 × 4 m room → 14 m of wall × 2.5 m = 35 m², minus a door and a window = 31.7 m², × 2 coats = 63.3 m², ÷ 10 m²/L = 6.3 litres.
Paint for common room sizes
The table is worked out by the paint calculator itself, with the same rule and defaults:
| Room (floor size) | Wall height | Wall area to paint | Paint (litres) | Paint (US gallons) |
|---|---|---|---|---|
| 10 × 10 ft | 8 ft | 288 ft² | 6.23 L | 1.65 gal |
| 10 × 10 ft | 10 ft | 368 ft² | 7.96 L | 2.1 gal |
| 10 × 12 ft | 8 ft | 320 ft² | 6.92 L | 1.83 gal |
| 10 × 12 ft | 10 ft | 408 ft² | 8.83 L | 2.33 gal |
| 12 × 12 ft | 8 ft | 352 ft² | 7.61 L | 2.01 gal |
| 12 × 12 ft | 10 ft | 448 ft² | 9.69 L | 2.56 gal |
| 12 × 14 ft | 8 ft | 384 ft² | 8.31 L | 2.19 gal |
| 12 × 14 ft | 10 ft | 488 ft² | 10.56 L | 2.79 gal |
| 15 × 20 ft | 8 ft | 528 ft² | 11.42 L | 3.02 gal |
| 15 × 20 ft | 10 ft | 668 ft² | 14.45 L | 3.82 gal |
| 3 × 3 m | 2.5 m | 26.7 m² | 5.33 L | 1.41 gal |
| 3 × 4 m | 2.5 m | 31.7 m² | 6.33 L | 1.67 gal |
| 4 × 5 m | 2.5 m | 41.7 m² | 8.33 L | 2.2 gal |
Walls only, 2 coats, one door and one window taken off. Rooms in feet: 350 ft²/gal, door 36 × 80 in, window 36 × 48 in. Rooms in metres: 10 m²/L, door 900 × 2,100 mm, window 1,200 × 1,200 mm. Add the ceiling, primer or your tin size in the calculator above.
How far does a litre (or a gallon) go?
Coverage depends on the type of paint. These are the figures the calculator fills in; they are on the safe side of what most tins say:
| Type of paint | Metric | US |
|---|---|---|
| Wall or ceiling paint (emulsion, plastic emulsion, distemper) | 10 m²/L | 350 ft²/gal |
| Outside walls (weather paint) | 8 m²/L | 300 ft²/gal |
| Textured paint | 5 m²/L | 200 ft²/gal |
| Enamel or gloss (doors, windows, grills, wood) | 12 m²/L | 400 ft²/gal |
| Primer or sealer only | 7 m²/L | 300 ft²/gal |
The typical coverage the calculator fills in for each type — on the safe side. If your tin gives a figure, use that one.
If your tin gives its own figure (for example "up to 13 m²/L" or "400 ft²/gal"), use that one — but treat "up to" as the best case on a smooth, sealed wall.
What makes you need more paint
- New plaster or bare drywall soaks up the first coat. Seal it with a mist coat or primer first, otherwise you will need a third coat.
- Rough surfaces (textured walls, woodchip, brick, exterior render) can need 20–40 % more than a smooth wall.
- A big colour change — dark over light or light over dark — usually needs a third coat, or a tinted primer.
- Rollers with a long nap hold more paint and put more on the wall than a short-nap roller.
- Ceilings are often forgotten: a 12 × 12 ft ceiling is another 144 ft² per coat.
Which tin sizes to buy
Round up to whole tins, and mix the sizes to waste the least:
- US: paint is sold in quarts (¼ gal), gallons and 5-gallon buckets. For 2.3 gallons buy two gallons and one quart, or three gallons if you want spare for touch-ups.
- UK and Europe: wall paint comes in 2.5 L, 5 L and 10 L tins. For 6.3 L, one 5 L tin plus one 2.5 L tin (7.5 L) is the usual choice.
Keep a little left over, labelled with the room and the date: it is the easiest way to touch up scuffs later.
Frequently asked questions
How many square metres does 1 litre of paint cover?
About 10 m² per coat for ordinary emulsion on a smooth wall. Exterior paint covers about 8 m², textured paint about 5 m², and gloss about 12 m². Your tin's own figure comes first.
How much paint do I need for a 10 × 12 room?
With 8 ft walls, one door and one window, and two coats: about 1.8 US gallons (6.9 litres). With 10 ft walls: about 2.3 gallons.
Do I need two coats of paint?
Usually yes. One coat is enough only when you repaint in the same colour over a wall in good condition. New plaster, patches and colour changes need two coats, sometimes three.
Should I include the doors and windows?
Take them off the wall area. A door is about 20 ft² (1.9 m²), a window 12–15 ft² (1.4 m²). If you also paint the door and frames, count them separately with gloss or trim paint.
Can I use the calculator for ceilings?
Yes: the paint calculator has a ceiling option, so it adds the ceiling's area to the walls.
Calculators in this guide
Enter your own sizes for an exact answer.
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