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How Many Gallons of Paint for a 12x12 Room
A wall-paint chart for 10×10, 10×12, 12×12, and 12×14 rooms, computed with the same formula as the paint coverage calculator.
A 12×12 room at the calculator's defaults needs 2.06 gallons, so you buy 3 gallons. Those defaults are 9 ft ceilings, 2 doors, 2 windows, 2 coats, and 350 square feet per gallon. The ceiling is not in that number.
Open the Paint Coverage Calculator if your room is a different height, or if the can prints a coverage number other than 350. The tables below are that form, run on four floor sizes. Every figure is the formula on that page. Nothing here is a store average or a "typical house" survey.
Assumptions, all of them
The calculator does not start from the floor. It starts from the walls.
- Perimeter = 2 × (length + width).
- Gross wall area = perimeter × ceiling height.
- Each door subtracts 21 square feet. That is the form's stand-in for a 3 ft by 7 ft door, not a measurement of your door.
- Each window subtracts 15 square feet. That is the form's stand-in for a rough 3 ft by 5 ft window.
- Paintable area = gross wall minus openings, and it will not go below zero.
- Coverage needed = paintable area × number of coats.
- Gallons = coverage needed ÷ square feet per gallon. The buy line is that decimal rounded up to the next whole gallon.
The form opens with height 9, doors 2, windows 2, coats 2, and coverage 350. Those are the inputs in the main table. Change any of them on the calculator and the gallons change with them. There is no extra waste percent beyond that round-up. Primer, ceiling, trim, and the faces of doors you paint are not in the wall gallons.
Gallons for 10×10, 10×12, 12×12, and 12×14
Two doors and two windows subtract 2 × 21 + 2 × 15 = 72 square feet in every row. Two coats. 350 square feet per gallon. Ceiling height 9 ft.
| Room | Floor | Perimeter | Gross wall | Paintable | Two coats | Gallons | Buy |
|---|---|---|---|---|---|---|---|
| 10×10 | 100 sq ft | 40 ft | 360 sq ft | 288 sq ft | 576 sq ft | 1.65 | 2 gal |
| 10×12 | 120 sq ft | 44 ft | 396 sq ft | 324 sq ft | 648 sq ft | 1.85 | 2 gal |
| 12×12 | 144 sq ft | 48 ft | 432 sq ft | 360 sq ft | 720 sq ft | 2.06 | 3 gal |
| 12×14 | 168 sq ft | 52 ft | 468 sq ft | 396 sq ft | 792 sq ft | 2.26 | 3 gal |
The 12×14 row is the calculator's own worked example: gross wall 468, openings 72, paintable 396, two coats 792, 792 ÷ 350 = 2.26, buy 3. The 12×12 row is the same arithmetic on a square floor. Floor area of 144 square feet is not the paint quantity. The walls are 432 square feet before the doors and windows come out.
Walk the 12×12 line once so the table is checkable. Perimeter = 2 × (12 + 12) = 48 ft. Gross wall = 48 × 9 = 432. Openings = 72. Paintable = 360. Two coats need 720 square feet of coverage. 720 ÷ 350 = 2.057, which the page shows as 2.06 gallons. The buy line uses the unrounded value and rounds up, so 3 gallons. One coat on the same walls is 360 ÷ 350 = 1.03 gallons, which still rounds up to 2. Three coats are 1,080 ÷ 350 = 3.09 gallons, which round up to 4.
Same rooms, 8 ft ceilings
The form's height field starts at 9. If you measure 8 ft and leave the other defaults alone, every room in the chart rounds up to 2 gallons. The 12×12 room is the one that changes purchase quantity: 1.78 gallons instead of 2.06, so 2 to buy instead of 3.
| Room | Gross wall | Paintable | Two coats | Gallons | Buy |
|---|---|---|---|---|---|
| 10×10 | 320 sq ft | 248 sq ft | 496 sq ft | 1.42 | 2 gal |
| 10×12 | 352 sq ft | 280 sq ft | 560 sq ft | 1.6 | 2 gal |
| 12×12 | 384 sq ft | 312 sq ft | 624 sq ft | 1.78 | 2 gal |
| 12×14 | 416 sq ft | 344 sq ft | 688 sq ft | 1.97 | 2 gal |
Measure the wall. An 8 ft guess in a 9 ft room is the difference between 2 and 3 gallons on the 12×12 row. The calculator will not infer the height from the floor size.
Bedroom and bathroom: same formula, different inputs
The tool has no bedroom preset and no bathroom preset. A bedroom that happens to match the defaults is already in the main table: an entry door, a closet door, and two windows are 2 doors and 2 windows, which is what the form starts with. That is a description of the inputs, not a claim about how bedrooms are built. If the closet is a pair of doors, or there is only one window, change the counts. Each extra door removes another 21 square feet before you divide by 350.
A bathroom is the same wall formula with the height and openings you type. Here are two small examples, labeled as examples. They are not a standard bath size.
| Example inputs | Gross wall | Openings | Paintable | Gallons | Buy |
|---|---|---|---|---|---|
| 1 door, 1 window | 208 sq ft | 36 sq ft | 172 sq ft | 0.98 | 1 gal |
| 1 door, 0 windows | 208 sq ft | 21 sq ft | 187 sq ft | 1.07 | 2 gal |
Perimeter of a 5×8 room is 2 × (5 + 8) = 26 ft. At 8 ft that is 208 square feet of wall. One door and one window remove 21 + 15 = 36, leaving 172. Two coats are 344 square feet. 344 ÷ 350 = 0.98 gallon, which rounds up to 1. Drop the window and the paintable area rises to 187, two coats are 374, and 374 ÷ 350 = 1.07, which rounds up to 2. The smaller opening count bought an extra gallon because 1.07 crossed a whole number. That is the round-up, not a different formula.
A slightly larger example, 8 ft by 10 ft, 8 ft ceiling, 1 door, 1 window, 2 coats, 350 square feet per gallon: gross wall 288, openings 36, paintable 252, two coats 504, 504 ÷ 350 = 1.44 gallons, buy 2. Type your own length and width if the room is not one of these.
The 15 square foot window is a stand-in. A glass shower wall or a wide bath window is not 15 square feet. Count it as extra windows, or measure it, the same way the calculator's slider example treats a 6 ft by 5 ft opening as two windows. Door faces, casing, and baseboard are still outside the gallon total.
The ceiling is a second purchase
Ceiling area is the floor rectangle. For the 12×12 room that is 144 square feet. One coat at 350 square feet per gallon is 144 ÷ 350 = 0.41 gallon, which rounds up to 1 gallon to buy. Two coats are 288 ÷ 350 = 0.82 gallon, still 1 gallon to buy. Do not add the ceiling into the wall gallons and then round once. The walls and the ceiling are separate cans if the color or the sheen differs. The Square Footage Calculator is the floor (and ceiling) check. The paint tool will not paint the ceiling for you.
When 350 is the wrong coverage number
350 is the value sitting in the coverage field when the page loads. It is not a measured rate for your wall. The label on the can is the number to type. The calculator's own notes say many interior latex labels quote about 350 to 400 square feet per gallon on smooth, sealed surfaces, and that the page will use whatever you type. If you type a lower number, the gallons rise in proportion, because gallons = coverage needed ÷ that number. The article on how to read a paint label is about what the printed coverage is claiming. This chart does not apply a second discount on top of 350.
Primer is a separate pass. The wall calculator will not add it unless you run one coat with the primer's own coverage number and treat that result as primer only. Trim is separate too. A color change that needs a third finish coat is the three-coat line above, not a guessed extra percent.
What to type before you go to the store
- Measure length, width, and ceiling height in feet. 30 ft 6 in is 30.5, not 30.6.
- Count doors and ordinary windows. Split a very large opening into the 21 and 15 square foot units, or measure it.
- Use 2 coats unless you have a reason the calculator's one-coat option fits (a similar light color on a sealed wall).
- Replace 350 with the number on the can.
- Buy the rounded-up gallons for the walls. Buy the ceiling on its own line.
An L-shaped room is two rectangles. Run each one and add the gallons. A doorway shared by both rectangles should be subtracted once. The Sod Calculator is the lawn next to the house, not a paint tool. Price per gallon, after you know the quantity, is the Unit Price Calculator.
FAQ
How many gallons of paint does a 12x12 room need?
A 12 by 12 ft room at the calculator's defaults (9 ft walls, 2 doors, 2 windows, 2 coats, 350 square feet per gallon) needs 2.06 gallons, so the buy line is 3 gallons. The ceiling is not included.
Does the chart include the ceiling?
No. The paint calculator estimates walls only. Ceiling area is the floor rectangle. A 12 by 12 ceiling is 144 square feet, which is 0.41 gallon at 350 square feet per gallon for one coat, rounded up to 1 gallon to buy. Add that separately.
What if the ceiling is 8 feet?
The same four rooms, still with 2 doors, 2 windows, 2 coats, and 350 square feet per gallon, all round up to 2 gallons. The 12 by 12 room drops from 2.06 gallons (buy 3) at 9 feet to 1.78 gallons (buy 2) at 8 feet.
How do I use this for a bedroom or a bathroom?
The calculator has no bedroom or bathroom mode. A bedroom that matches the form defaults (entry door, closet door, two windows, 9 ft walls) is the main table. A bathroom is the same formula with the openings and height you measure. A 5 by 8 ft example at 8 ft, one door, and one window is 0.98 gallon, which rounds up to 1 gallon.
Why buy 3 gallons when the math says 2.06?
The calculator rounds up to the next whole gallon. 2.06 is just over 2, so the purchase quantity is 3. The extra is the unopened can, not a second coverage rate.
Key takeaways
- 12×12 at the form defaults is 2.06 gallons of wall paint, so buy 3.
- 10×10 is 1.65 gallons (buy 2). 10×12 is 1.85 (buy 2). 12×14 is 2.26 (buy 3).
- Those rows use 9 ft walls, 2 doors at 21 square feet, 2 windows at 15, 2 coats, and 350 square feet per gallon.
- At 8 ft, with the other defaults unchanged, all four rooms round up to 2 gallons.
- The ceiling is the floor area divided by coverage, bought separately.
Related
- Paint Coverage Calculator for a room that is not in the table
- How to read a paint label
- Square Footage Calculator for the floor and the ceiling
- Baking pan conversion chart if the same weekend includes a cake, not a wall