Work out how much paint you need for a room, say a 12×12 bedroom, or for a single wall. Enter room size or wall area and coats, and get gallons or litres with doors and windows subtracted and coverage you can adjust.
Enter the room size (the calculator finds wall area) or a wall area directly. Default coverage is about 350 ft² per gallon (≈11 m² per litre) per coat — adjust to match your paint’s label.
Paint needed = wall area × coats ÷ coverage. Coverage varies by paint, surface and colour — porous or dark-to-light changes need more. Buy a little extra for touch-ups and uneven surfaces.
How Much Paint Do I Need for a 12×12 Room?
A 12×12 room with 8 ft ceilings needs about 2.2 gallons for two coats. The four walls total 2 × (12 + 12) × 8 = 384 sq ft, two coats make 768 sq ft, and at 350 sq ft per gallon that is 2.19 gallons. Subtract doors and windows and it drops a little.
- Add length and width and double it: 2 × (12 + 12) = 48 ft of wall.
- Multiply by height: 48 × 8 = 384 sq ft.
- Multiply by coats: 384 × 2 = 768 sq ft.
- Divide by coverage: 768 ÷ 350 = 2.19 gallons.
Formula: In room mode, Wall area = (2 × (Length + Width) × Height) − Doors & windows area. In area mode, Wall area is entered directly. Total paint area = Wall area × Coats. Paint needed = Total paint area ÷ Coverage per unit, given in gallons (feet units, default 350 ft²/gal) or litres (metric, default 11 m²/L), with 1 gallon = 3.785411784 litres for converting between the two.
- Length, Width, Height: the room’s dimensions, used in Room size mode to find wall area automatically
- Wall area: a directly entered area, used instead of room dimensions in Wall area mode
- Doors & windows area: the combined area of openings to subtract from the wall area, optional
- Coats: the number of paint coats planned, defaulting to 2 if left blank
- Coverage / unit: the paint’s coverage rate per coat, defaulting to 350 ft²/gal or 11 m²/L, adjustable to match the label on your paint
Gallons and Litres for Common Rooms
A 12 × 10 ft room needs about 2 gallons for two coats. For how many litres of paint you need for a room, see the metric rows.
| Length | Width | Height | Openings | Coats | Coverage | Paint needed |
|---|---|---|---|---|---|---|
| 12 ft | 10 ft | 8 ft | 0 ft² | 2 | 350 ft²/gal | 2.01 gal |
| 15 ft | 12 ft | 9 ft | 40 ft² | 2 | 350 ft²/gal | 2.55 gal |
| 10 ft | 10 ft | 8 ft | 20 ft² | 1 | 300 ft²/gal | 1.00 gal |
| 6 ft | 5 ft | 8 ft | 15 ft² | 3 | 350 ft²/gal | 1.38 gal |
| 4 m | 3.5 m | 2.4 m | 0 m² | 2 | 11 m²/L | 6.55 L |
| 5 m | 4 m | 2.5 m | 2 m² | 2 | 11 m²/L | 7.82 L |
How Much Does a Gallon of Paint Cover in Square Feet?
Around 350 sq ft per coat is the usual figure, but use the coverage rate printed on the tin you plan to buy. Your estimate is only as accurate as that number, and thick or textured paints cover less.
Surface condition matters. Bare plaster, new drywall and rough masonry soak up paint, so they usually need a primer or mist coat first. Enter an extra coat when covering a dark colour with a light one.
- Measure every wall you will paint; the tool already subtracts the doors and windows you enter.
- Work out ceilings, trim and walls separately, as they often use different products.
- Buy all of one tinted colour in one go, since mixed batches can vary slightly.
Round the result up to the nearest tin size, and keep a little leftover for touch-ups. The Wikipedia article on paint explains binders, pigments and finishes. For a second room, run it again with its own measurements.
Common questions about how much paint to buy
How much paint do I need for a 12×12 room with 8 foot ceilings?
The walls come to 2 × (12 + 12) × 8 = 384 sq ft. Two coats at 350 sq ft per gallon need about 2.2 gallons, or about 1.97 gallons if you subtract 40 sq ft of doors and windows.How many gallons of paint do I need for a 10×10 room?
With 8 ft walls, a 10×10 room has 320 sq ft of wall. Two coats at 350 sq ft per gallon come to about 1.83 gallons, so two 1-gallon cans.How much does a gallon of paint cover in square feet?
About 350 sq ft per gallon per coat is a commonly cited average for interior wall paint, but brand, sheen and surface texture change it. Check the figure on your can and enter it in the Coverage field.How many coats of paint for interior walls?
Two coats is standard for most colour changes and is what the calculator uses if you leave Coats blank. A matching-colour touch-up may need one, while dark-to-light changes often need a third coat or a tinted primer.Should I subtract the ceiling from wall area?
No. The calculator only estimates wall area (perimeter × height). If you’re painting the ceiling too, measure it separately and add it in Wall area mode.How do I switch the result between gallons and litres?
Use the units toggle: Metres shows litres and Feet shows gallons. The results panel shows both figures whichever unit you enter measurements in.Related Calculators
Prefer wallpaper to paint for a feature wall? The wallpaper calculator covers roll counts using a similar area-based approach. If you haven’t measured the room yet, start with the square footage calculator, and for the floor once the walls are done, the tile quantity calculator can help plan materials. You may also find the Drywall Screw Calculator useful. For a related estimate, try the Drywall Mud Calculator. You may also find the Caulk Calculator useful.