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Paint coverage calculator
Put your room length, width, wall height, coats and coverage per gallon in: a 14 ft by 12 ft room with 8 ft walls and 2 coats needs 416 sq ft of wall, 832 sq ft of paint, 2.38 gallons exact, 3 gallons to buy.
★ CONSTRUCTION · PAINTING · COVERAGE
Paint Coverage Calculator: 3 Gallons for a 14x12 Room
On the defaults — a 14 ft by 12 ft room, 8 ft walls, 2 coats, 350 sq ft a gallon — you need 3 gallons, 2.38 exact. This is the paint coverage tool: measure the walls once, multiply by the coats, and order the paint once — a room one gallon short waits for no second coat.
What does paint coverage needed 3 gallons mean?
It means a 14 ft by 12 ft room with 8 ft walls has 416 sq ft of wall, and two coats over that wall need 832 sq ft of paint, which is 2.38 gallons at 350 sq ft a gallon — so you buy 3 gallons, since paint is sold by the whole gallon. The wall area is the perimeter times the height: 2 × (14 + 12) × 8 = 416. The coats multiply it, and the coverage divides it. The buy figure is the shopping number, while the exact figure is the planning number: 2.38 gallons tells you the third gallon is barely touched, so a room a little smaller would buy 2.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Wall area | 2 × (length + width) × height | 416 sq ft — 2 × (14 + 12) × 8. |
| Paint area | wall area × coats | 832 sq ft — 416 × 2. |
| Gallons exact | paint area ÷ coverage | 2.38 gallons — 832 ÷ 350. |
| Gallons to buy | exact, rounded up | 3 gallons — 2.38, rounded up. |
Three things to check before you trust the number
First, measure the walls you will actually paint, not the room on a plan: subtract large windows and doors if you want a tight figure, since this calculator counts the full wall area and a wall of glass paints far less. Second, read the coverage off your own can, not off a memory: primer, dark colours and rough plaster all cover less than the label headline. Third, remember the ceiling is not counted here — a ceiling painted too needs its own length × width added. For the price side of the same room, the paint cost calculator prices the gallons.
Worked example
14 ft long, 12 ft wide, 8 ft walls, 2 coats, 350 sq ft a gallon. Wall: 2 × (14 + 12) × 8 = 416 sq ft. Paint: 416 × 2 = 832 sq ft. Exact: 832 ÷ 350 = 2.38 gallons. Buy: 3 gallons. In practice that means buying 3 gallons, opening two, and keeping the third mostly full for touch-ups — the classic paint leftover, and far better than running dry halfway through the second coat.
Every branch, checked
With a 16 ft room instead of 14 ft, the wall rises to 448 sq ft and the paint to 896 sq ft, 2.56 gallons exact, still 3 gallons to buy. With 10 ft walls instead of 8 ft, the wall rises to 520 sq ft and the paint to 1040 sq ft, 2.97 gallons exact, still 3 gallons to buy — height is the dearest change, since it lifts every wall. With 1 coat instead of 2, the paint halves to 416 sq ft, 1.19 gallons exact, 2 gallons to buy. With 400 sq ft a gallon instead of 350, the exact falls to 2.08 gallons, still 3 gallons to buy. Length, height, coats and coverage each move the room on their own, so a wrong height figure is as costly as a wrong length.
The reverses, worked backwards
The length behind 3 gallons is 14 ft: at 10 ft the need is 3 gallons (10 ft long, 12 ft wide, 8 ft walls, 352 sq ft wall, 2 coats, 704 sq ft paint, 350 sq ft a gallon, 2.01 gallons exact); at 18 ft it is 3 gallons (18 ft long, 12 ft wide, 8 ft walls, 480 sq ft wall, 2 coats, 960 sq ft paint, 350 sq ft a gallon, 2.74 gallons exact). The coats behind 3 gallons are 2: at 1 coat the need is 2 gallons (14 ft long, 12 ft wide, 8 ft walls, 416 sq ft wall, 1 coat, 416 sq ft paint, 350 sq ft a gallon, 1.19 gallons exact); at 3 coats it is 4 gallons (14 ft long, 12 ft wide, 8 ft walls, 416 sq ft wall, 3 coats, 1248 sq ft paint, 350 sq ft a gallon, 3.57 gallons exact). The coverage behind 3 gallons is 350 sq ft a gallon: at 300 sq ft a gallon the need is 3 gallons (14 ft long, 12 ft wide, 8 ft walls, 416 sq ft wall, 2 coats, 832 sq ft paint, 300 sq ft a gallon, 2.77 gallons exact); at 400 sq ft a gallon it is 3 gallons (14 ft long, 12 ft wide, 8 ft walls, 416 sq ft wall, 2 coats, 832 sq ft paint, 400 sq ft a gallon, 2.08 gallons exact). Each reverse moves one input and holds the rest, so the step is exactly one length, coat or coverage change.
What the defaults assume
The defaults assume a rectangular 14 ft by 12 ft room, 8 ft walls, 2 coats, and 350 sq ft a gallon. They do not assume doors, windows, ceilings, primer, or a colour change that needs a third coat — a dark wall painted light often needs that third coat, and a wall of windows paints far less than its full area.
Who uses this
- A homeowner repainting a bedroom: the 3-gallon buy settles the paint order before the first roller is loaded.
- A painter quoting a room: the wall, paint and exact figures off the calculator are the lines on the quote, not a guess.
- A DIY decorator on a budget: the exact figure shows whether the room is a 2-gallon or a 3-gallon room, so the third gallon is a choice, not a surprise.
- A landlord refreshing between tenants: the same maths on every room size gives the paint order for the whole flat in one pass.
Accuracy & limitations
The arithmetic is exact for the inputs entered; the judgement is the coverage and the deductions. Real cans cover less on rough plaster and dark colours, and real rooms lose wall to doors and windows — the tape on the wall overrides any planning figure. Treat 3 gallons as the planning buy for a 14 ft by 12 ft room at 8 ft walls and 2 coats, and check the can label for the paint you actually bought before ordering.
Cite this calculator
Bright Side Kit, “Paint Coverage Calculator: 3 Gallons for a 14x12 Room”, https://brightoolbox.com/paint-coverage-calculator/, accessed 3 November 2026. Students and researchers: cite the calculator name, the page URL and the date you used it, and quote the defaults (14 ft long, 12 ft wide, 8 ft walls, 2 coats, 350 sq ft a gallon) so the 3-gallon result can be checked.
Frequently asked questions
How much paint do I need for a 14x12 room?
3 gallons at 8 ft walls and 2 coats: 416 sq ft of wall, 832 sq ft of paint, 2.38 gallons exact at 350 sq ft a gallon, rounded up to 3 gallons to buy.
How do I work out paint coverage for a room?
Multiply the perimeter by the height for wall area, multiply by coats for paint area, then divide by coverage per gallon. A 14 ft by 12 ft room at 8 ft walls is 416 sq ft of wall; two coats are 832 sq ft of paint.
Why round the gallons up?
Because paint is sold by the whole gallon: 2.38 gallons exact means two full gallons plus most of a third, so the shop sells you 3. The leftover third gallon is your touch-up paint.
Does a second coat double the paint?
Yes, near enough: two coats paint the same wall twice, so 416 sq ft of wall needs 832 sq ft of paint. A primer coat on bare plaster is a third pass on top of that.
Should I subtract doors and windows?
For a tight order, yes: this calculator counts the full wall area, so a wall of glass over-counts. Measure the door and window areas and subtract them from the wall area before dividing by coverage.
What if my walls are taller than 8 ft?
Height lifts every wall at once: the same 14 ft by 12 ft room at 10 ft walls has 520 sq ft of wall and needs 1040 sq ft of paint, 2.97 gallons exact, still 3 gallons to buy.