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Paint Calculator
Add each room with its length, width, wall height, doors and windows, and say whether the ceiling is painted too. Enter the coats and the coverage on your can. You get the wall and ceiling area, the gallons needed and how many to buy. Two rooms with two coats need about 5.1 gallons, so 6.
Updated · Sources re-checked by
Walls 453 sq ft
Walls 316 sq ft, ceiling 120 sq ft
5.08 gallons
| Walls | 769 sq ft |
| Ceilings | 120 sq ft |
| Paint to cover (2 coats) | 1,778 sq ft |
| Buy, whole gallons | 6 |
| Buy, to the nearest quart | 5.25 gallons |
A door counts as 21 sq ft and a window as 15. Use the coverage printed on your can. Nothing you type is saved or sent anywhere.
How the paint calculator works
Wall area = 2 × (length + width) × height, minus 21 sq ft for each door (3 × 7 ft) and 15 sq ft for each window (3 × 5 ft). Ceiling area = length × width, if you paint it. Paint to cover = (walls + ceilings) × coats. Gallons = that ÷ the coverage per gallon on the can, which is about 350 sq ft for smooth interior walls. You buy whole gallons, so round up, or to the next quart.
| Room | Wall area | Gallons for 2 coats |
|---|---|---|
| 10 × 10 ft | 320 sq ft | 1.83 |
| 12 × 12 ft | 384 sq ft | 2.19 |
| 12 × 16 ft | 448 sq ft | 2.56 |
| 15 × 20 ft | 560 sq ft | 3.2 |
| Opening | Size used | Area |
|---|---|---|
| Door | 3 × 7 ft | 21 sq ft |
| Window | 3 × 5 ft | 15 sq ft |
| Large window or sliding door | count as 2 | 30 to 42 sq ft |
Worked example: a living room and a bedroom with a painted ceiling
- Living room: 2 × (16 + 12) × 9 = 504 sq ft, minus 1 door (21) and 2 windows (30) leaves 453 sq ft.
- Bedroom: 2 × (12 + 10) × 8 = 352, minus 1 door and 1 window (36) leaves 316 sq ft, plus a 120 sq ft ceiling.
- Total to paint: 889 sq ft. Two coats: 1,778 sq ft of paint to cover.
- Gallons: 1,778 ÷ 350 = 5.08, just over 5.
- Buy 6 gallons. At $40 a gallon that is $240.00.
Common questions
How much paint do I need for a room?
Work out the wall area, take off the doors and windows, multiply by the number of coats and divide by the coverage on the can. A 12 × 12 ft room with 8 ft walls is 384 sq ft of wall, so about 2.2 gallons for two coats before the doors and windows come off.
Do I paint the ceiling and trim with the same paint?
Usually not. Ceilings often use a flat ceiling paint and trim a harder gloss, so run them as separate jobs. Tick the ceiling box here only when the ceiling gets the same paint as the walls.
How many coats should I plan for?
Two is the usual number for a color change. One coat can be enough over a similar color or when the paint has primer built in. A big color change may need more.
What coverage should I use?
The can's label. About 350 to 400 sq ft per gallon per coat is typical for smooth interior walls, and rough or dark surfaces cover less. The box starts at 350, and you can change it.
Should I count the doors and windows?
Yes. Taking them off saves a lot of paint on a room with big windows. This page uses 21 sq ft per door and 15 per window, so count a large opening as two.
Why does the calculator say to buy more than I need?
Paint is sold in quart, gallon and 5-gallon cans. Buying whole gallons gives you touch-up paint, and mixing a second batch later can change the color slightly.
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Sources
- How much area does a gallon of paint cover: about 350 to 400 sq ft per coat; the can's label is the real figure (checked October 28, 2026)
This calculator is an estimate for planning. Coverage depends on the paint, the surface and how you apply it, so check the can and ask the paint store before you buy.