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Paint calculator
Put your room size and coats in: a 12 ft by 10 ft room with 8 ft ceilings has 352 sq ft of wall, and 2 coats need 2.01 gallons — buy 3.
★ CONSTRUCTION · PAINT · ROOM
Paint Calculator: 2.01 Gallons, 2 Coats, 12×10 Room
On the defaults — a 12 ft by 10 ft room, 8 ft ceilings, 2 coats — you need 2.01 gallons, so buy 3. This is the paint tool: measure the room once, and walk into the shop knowing the tin count, not guessing it in the aisle.
What does paint needed 2.01 gallons mean?
It means the walls of this room, painted twice, drink just over two gallons of paint — and because paint is sold by the gallon, you buy three and keep the rest for touch-ups. The wall area is the whole story: two long walls of 12 by 8 ft and two short walls of 10 by 8 ft add to 352 sq ft, and two coats double that to 704 sq ft of painted surface. At 350 sq ft a gallon, that is 2.01 gallons. The rounding-up matters more than the decimal: a half-gallon short at the end of the second coat is a second trip to the shop, while a spare gallon lives in the garage for scuffs.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Wall area | 2 × (length + width) × height | 352 sq ft — 2 × (12 + 10) × 8. |
| Painted surface | wall area × coats | 704 sq ft — 352 × 2. |
| Paint needed | painted surface ÷ 350 sq ft per gallon | 2.01 gallons — 704 ÷ 350. |
| Buy | round up to whole gallons | 3 gallons — the spare covers touch-ups. |
Three things to check before you trust the number
First, check the coverage figure on your tin: 350 sq ft a gallon is a common emulsion rate, but a thick paint or a rough wall can drop it to 300, which would push this room to 2.35 gallons — still 3 tins, but with less spare. Second, decide whether doors and windows come off the area: this calculator sizes the full walls, and a standard door saves only about 0.12 gallons over two coats, so it rarely changes the tin count. Third, remember primer is separate: a dark-to-light change may need a primer coat first, and that coat is paint too, just not the colour coat counted here.
Worked example
12 ft long, 10 ft wide, 8 ft ceilings, 2 coats. Wall area: 2 × (12 + 10) × 8 = 352 sq ft. Painted surface: 352 × 2 = 704 sq ft. Paint needed: 704 ÷ 350 = 2.01 gallons. Buy 3 gallons. In practice that means two gallons go on the walls and the third sits mostly unused — until the first scuff, when it becomes the most valuable gallon in the house. If the same room had 9 ft ceilings, the area would be 396 sq ft and the need 2.26 gallons — still 3 tins, so the ceiling height would not change the shop list, only the spare.
Every branch, checked
With a 14 ft long room instead of 12 ft, the area rises to 384 sq ft and the need to 2.19 gallons — still 3 tins. With 9 ft ceilings, the area rises to 396 sq ft and the need to 2.26 gallons — still 3 tins. With 1 coat instead of 2, the need falls to 1.01 gallons — buy 2 tins, since one tin is 0.01 gallons short. With 3 coats, the need rises to 3.02 gallons — buy 4 tins, since three tins fall 0.02 gallons short. The tin count is a step function: small changes in area often change nothing, until they cross a whole gallon.
The reverses, worked backwards
The length behind 2.01 gallons is 12 ft: at 10 ft the need is 1.83 gallons (buy 2); at 14 ft it is 2.19 gallons (buy 3). The width behind 2.01 gallons is 10 ft: at 8 ft the need is 1.83 gallons (buy 2); at 12 ft it is 2.19 gallons (buy 3). The height behind 2.01 gallons is 8 ft: at 7 ft the need is 1.76 gallons (buy 2); at 9 ft it is 2.26 gallons (buy 3). The coats behind 2.01 gallons are 2: at 1 coat the need is 1.01 gallons (buy 2); at 3 coats it is 3.02 gallons (buy 4). Each reverse moves one input and holds the rest, so the step is exactly one dimension or one coat.
What the defaults assume
The defaults assume a 12 ft by 10 ft room with 8 ft ceilings, two coats, and 350 sq ft of coverage per gallon on smooth walls. They do not assume doors and windows subtracted, textured walls, a primer coat, or the ceiling painted — paint the ceiling too and add its 120 sq ft, which at two coats adds 0.69 gallons and may push the buy to 4 tins.
Who uses this
- A homeowner repainting a bedroom: the 3-gallon buy settles the shop list before the first tin is opened.
- A renter freshening one room: the 2.01-gallon figure shows one coat is not enough and two coats is exactly three tins.
- A landlord turning a flat between tenants: the same maths per room, times the room count, prices the whole repaint.
- A decorator quoting a job: wall area first, coats second, tins third — the quote follows the same three steps.
Accuracy & limitations
The arithmetic is exact for the inputs entered; the judgement is the coverage rate. Real walls drink paint unevenly: fresh plaster and rough texture take more, a previously painted smooth wall takes less, and a dark colour over a light one can need the third coat this calculator only counts if you ask for it. Treat 2.01 gallons as the planning figure and the 3-tin buy as the safe shop list; if the tin states a different coverage, re-run with that rate in mind — the area maths does not change, only the division.
Cite this calculator
Bright Side Kit, “Paint Calculator: 2.01 Gallons, 2 Coats, 12×10 Room”, https://brightoolbox.com/paint-calculator/, accessed 2 November 2026. Students and researchers: cite the calculator name, the page URL and the date you used it, and quote the defaults (12 ft × 10 ft room, 8 ft ceilings, 2 coats, 350 sq ft per gallon) so the 2.01-gallon result can be checked.
Frequently asked questions
How much paint do I need for a 12×10 room?
2.01 gallons for two coats — buy 3 gallons. The walls total 352 sq ft, two coats make 704 sq ft of painted surface, and at 350 sq ft a gallon that is 2.01 gallons, rounded up to whole tins.
How many square feet does a gallon of paint cover?
About 350 sq ft for a typical emulsion on smooth walls, which is the rate this calculator uses. Check your tin: thick paint or rough walls can drop it to 300 sq ft, which raises the need but rarely the tin count on a room this size.
Should I subtract doors and windows from the wall area?
For a shop list, no: a standard door saves only about 0.12 gallons over two coats, so it almost never changes the tin count. For a precise quote, subtract each opening — about 21 sq ft per door, 15 sq ft per window — before dividing by coverage.
Is one coat enough?
Almost never for a colour change: one coat on this room needs 1.01 gallons, so you still buy 2 tins, and the finish will show through. Two coats is the normal finish; the second coat is what makes the colour even.
Do I need primer too?
For a dark-to-light change or fresh plaster, yes — and primer is a separate coat, not counted in the colour coats here. Price it with the paint cost calculator, which handles the money side of the same room.
What if I am also painting the ceiling?
Add the ceiling area — 12 × 10 = 120 sq ft — to the wall area first. At two coats that adds 0.69 gallons, taking this room to 2.70 gallons, still 3 tins but with much less spare.