Paint Calculator
Use this free paint calculator to find out exactly how much paint you need for any room. Enter your room's length, width, and wall height, subtract doors and windows, and get an instant gallon estimate with a full cost breakdown — no guesswork, no extra trips to the store.
Advanced options
How to Use the Paint Calculator
- Measure your room: Enter the room's length, width, and wall height in feet. You only need the floor dimensions and ceiling height — the calculator works out total wall area automatically.
- Count doors and windows: Enter how many doors and windows are on the walls you're painting. The calculator subtracts standard sizes (21 sq ft per door, 15 sq ft per window) so you don't overbuy paint.
- Choose your coats: Most rooms need two coats for even, solid color. Select one coat only if you're using a paint-and-primer product over a similar existing color.
- Read your results: The calculator shows exactly how many gallons to buy, a full area breakdown, and an estimated cost if you enter a price per gallon.
What Is This Paint Calculator?
This paint calculator is a free tool that tells you how much paint to buy for a room. Instead of guessing or overbuying "just in case," you enter your room's measurements and get a precise gallon count based on the actual wall area you're painting.
Why Use a Paint Calculator?
Buying too little paint means an extra trip to the store mid-project, and colors can vary slightly between batches. Buying too much wastes money on paint you'll never use. A paint quantity calculator solves both problems by working out the real paintable area — wall area minus doors and windows — before you shop.
How Does This Calculator Work?
The calculator uses a standard formula for estimating room painting: it finds the total wall area (perimeter × height), subtracts the area taken up by doors and windows, multiplies by your number of coats, and divides by how many square feet a gallon of your paint covers.
Gallons = ((Wall Area − Doors − Windows) × Coats) ÷ Coverage per Gallon
The result is then rounded up to the nearest whole gallon, since paint is sold by the can.
Worked Example: How Much Paint for a 12x10 Room?
Take a bedroom that is 12 feet long, 10 feet wide, with 8 foot walls, one door, and two windows, painted with two coats:
- Perimeter: 2 × (12 + 10) = 44 ft
- Gross wall area: 44 × 8 = 352 sq ft
- Subtract openings: 352 − 21 (door) − 30 (2 windows) = 301 sq ft
- Apply two coats: 301 × 2 = 602 sq ft of coverage needed
- Divide by coverage rate: 602 ÷ 350 ≈ 1.72 gallons
- Round up: Buy 2 gallons
Load this example in the calculator above.
Paint Coverage Tips
- Textured or unprimed walls absorb more paint. Lower your coverage rate to around 250–300 sq ft per gallon if your walls are textured, unprimed drywall, or brick.
- Going from dark to light (or a big color change) often needs a third coat or a tinted primer first.
- Ceilings are usually painted separately with flat ceiling paint — use the "Include ceiling" option only if you're using the same paint for both.
- Buy a little extra if you plan to do touch-ups later, since paint batches can vary slightly in color over time.
Paint Calculator FAQs
It depends on your wall area and how many coats you plan to apply. As a rule of thumb, one gallon of paint covers about 350 square feet with a single coat. For a typical 12x10 foot bedroom with 8 foot ceilings and two coats, you need about 2 gallons after subtracting the door and windows. Enter your room's measurements above for an exact number.
Most interior paints cover 350 to 400 square feet per gallon on a smooth wall with a single coat. Textured, unprimed, or very absorbent walls can reduce coverage to 250 to 300 square feet per gallon. Check the coverage rate printed on your specific paint can and adjust the coverage field in the calculator if it differs from the default of 350.
Yes. Doors and windows are not painted the same way as walls, so subtracting their area gives a more accurate estimate. This calculator automatically subtracts 21 square feet for each standard door and 15 square feet for each standard window from the total wall area.
Two coats are standard for most interior walls, especially when changing colors or painting over a darker shade. One coat may be enough when using a high-quality paint-and-primer-in-one on a wall that is already a similar color. Three coats are sometimes needed for very light colors over dark surfaces, like white over red.
For a 10x10 foot room with 8 foot ceilings, the gross wall area is about 320 square feet. After subtracting a typical door and window, the paintable area is roughly 284 square feet. One gallon (covering about 350 square feet) is enough for a single coat, but you will need close to 2 gallons for two coats.
Only if you are painting the ceiling in the same color or with the same amount of paint. Ceilings are usually painted with ceiling-specific paint and calculated separately. Check the "Include ceiling" option in the calculator if you want the ceiling area added to your wall total.
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