Paint Calculator: Gallons for Walls and Ceilings
Enter the room size (or the wall area), take off the doors and windows, pick the number of coats and the coverage of your paint, and get the gallons to buy for the walls, the ceiling and a primer coat, rounded up to whole gallons and to the quart, plus the cost at your price per gallon.
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Result
Enter your numbers to see the result.
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Read the how-to guide
The math
- Wall area = 2 × (length + width) × ceiling height, or the area you enter.
- Subtract 21 sq ft for each door and 15 sq ft for each window, the usual estimating allowances.
- Gallons = area × coats ÷ coverage per gallon. The ceiling (length × width) is figured the same way, and a primer coat is one coat over everything being painted.
- Buy whole gallons, or gallons plus quarts where the store sells them; the calculator shows both. Cost = gallons bought × price.
Coverage on the can assumes a smooth, sealed surface. Bare drywall, plaster patches, texture and masonry soak up more, and a color change from dark to light or to a deep red or yellow usually needs an extra coat or a tinted primer.
Worked example
A 14 × 12 ft room with 8 ft ceilings has 2 × (14 + 12) × 8 = 416 sq ft of wall. Less one door (21) and two windows (30) leaves 365 sq ft. Two coats at 350 sq ft per gallon take 365 × 2 ÷ 350 = 2.09 gallons, so buy 3 gallons (or 2 gallons and 1 quart). The 168 sq ft ceiling takes 0.96 gallon for two coats, so 1 gallon. At $35 a gallon the 4 gallons cost $140.
Frequently asked questions
How much does a gallon of paint cover?
About 350 to 400 sq ft per coat on a smooth, previously painted wall. Rough, porous or textured surfaces, and spraying, use more: figure 250 to 300 sq ft per gallon, and check the number on the can.
Do I really need two coats?
Usually, yes. One coat covers when the new color is close to the old one and the paint is a premium paint-and-primer product. Two coats give an even sheen and full color, and a dark-to-light change or a bright red may take three or a tinted primer.
When do I need primer?
On bare drywall or plaster, patched areas, stained or glossy surfaces, raw wood and big color changes. Previously painted walls in good condition that are getting a similar color can usually skip it.
Should I include closets and trim?
Add the closet walls to the area if you are painting them. Trim, doors and windows are painted separately, usually with a quart to a gallon of trim paint per room.
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This calculator gives an estimate for planning and is not tax, legal or engineering advice. Confirm code-related results against the code edition adopted in your jurisdiction and with your authority having jurisdiction, and follow the manufacturer's instructions.