Paint Calculator
Enter your room size, doors, windows and number of coats to see how much paint to buy, in gallons and quarts.
- Walls & ceiling
- Doors & windows
- Coats & coverage
- Gallons, quarts & litres
Paint for a room
Fill in the boxes. The answer appears as you type.
How much paint do you need?
Paint is sold by the gallon, and one gallon typically covers 350–400 square feet with one coat on smooth, primed walls. To estimate paint, work out the wall area (perimeter × height), subtract about 21 sq ft per door and 15 sq ft per window, add the ceiling if you are painting it, multiply by the number of coats and divide by the coverage on the can. This calculator does that and rounds up to the nearest quart so you buy enough without large leftovers.
How to use Paint Calculator
- Measure the room’s length and width and the wall height.
- Count doors and windows.
- Set the number of coats (usually 2) and the coverage from the paint can.
- Choose walls only or walls and ceiling, then read how much to buy.
Paint estimating tips
- Coverage: 350–400 sq ft per gallon on smooth walls; 250–300 on textured or unprimed surfaces.
- Two coats are standard; dramatic colour changes may need primer plus two coats.
- A door is about 21 sq ft (3 × 7 ft); a window about 15 sq ft.
- Keep a little extra for touch-ups.
Why use this paint calculator
- Answers as you typeNo Calculate button. Change any number and every result updates instantly.
- Shows the workingEach answer has a plain-English sentence, the steps and a formula for Excel or Google Sheets.
- Buy the right amountResults are in the units stores sell (gallons, squares, bundles, BTU sizes), with sensible allowances built in.
- PrivateYour numbers are calculated on your device and never sent anywhere.
Common uses
- Bedrooms and living rooms. A standard 12 × 10 room with two coats.
- Ceilings. Include the ceiling in the same estimate.
- Colour changes. Add a coat for dark-to-light changes.
- Budgeting. Know how many gallons to price.
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Example: a 12 × 10 ft bedroom
Walls 2 × (12 + 10) × 8 = 352 sq ft − 1 door (21) − 2 windows (30) = 301 sq ft. Two coats at 350 sq ft/gal = 1.72 gallons → buy 1 gallon and 3 quarts.
What to expect from the result
Estimates assume flat walls and the coverage you enter. Textured, porous or very dark surfaces use more paint. Trim, cabinets and doors themselves are not included.
Paint Calculator questions
How much paint do I need for a 12 × 12 room?
About 1.9 gallons for two coats on 8 ft walls with one door and two windows, so buy 2 gallons.
How many square feet does a gallon of paint cover?
Usually 350–400 sq ft per coat on smooth, primed walls. Check the can for your paint.
Do I need two coats of paint?
Usually yes, for even colour and durability. One coat may be enough when repainting the same colour with quality paint.
Should I subtract doors and windows?
Yes for large rooms; it can save a quart or more. For small rooms the difference is minor.
How much paint for a ceiling?
Ceiling area is length × width. A 12 × 10 ceiling (120 sq ft) needs about 0.7 gallons for two coats.