Paint calculator
Estimate gallons of paint for walls, ceilings and rooms, accounting for doors, windows and multiple coats.
Paint calculator
Estimate gallons of paint for walls, ceilings and rooms, accounting for doors, windows and multiple coats.
Enter your wall dimensions to see the paint estimate.
Gallons needed
Project summary
How it works
These are estimates for planning. Actual paint coverage varies by surface texture, porosity and application method.
Paint calculator
The calculation is straightforward
Measure each wall by multiplying its length by its height. Add up the wall areas, subtract the doors and windows, and you have the paintable square footage. Divide by the coverage rate on the paint can, multiply by the number of coats, and you have gallons. The reason people get this wrong is not the math but the assumptions: walls are never perfectly flat, paint coverage varies with color and surface, and a roller lays down more paint than a sprayer.
Coverage depends on everything
The paint can says 350 to 400 square feet per gallon, and that number is true under ideal conditions: smooth drywall, one coat of primer, and a roller with the right nap. In practice, dark colors over light surfaces need more coats, textured surfaces absorb more paint, and new drywall drinks primer before it takes finish. A planning figure of 350 square feet per gallon for eggshell latex on smooth drywall is conservative enough to keep you from running short.
Why two coats is usually the answer
One coat almost never gives even coverage, especially with color changes. The first coat seals and tints; the second evens out the color and hides the surface underneath. Primer counts as a coat if you are using it, but the calculator treats it as separate because primer coverage is typically higher than finish coverage. For the ceiling, one coat is often enough if the color is not changing.
Frequently asked questions
How many square feet does a gallon of paint cover?
About 350 square feet on smooth drywall with a roller, though the paint can may claim 400 to 450. Textured surfaces, dark colors, and bare drywall reduce that number. A safe planning figure for most interior walls is 350 square feet per gallon per coat.
How much paint do I need for a 12 by 12 room?
A 12 by 12 room with 8-foot walls has about 384 square feet of wall area. Subtract 60 square feet for a door and two windows, and you have 324 paintable square feet. At 350 square feet per gallon and two coats, you need about 1.85 gallons, so buy 2 gallons. For the ceiling at 144 square feet, one gallon covers it in one coat.
How many gallons of paint for a 12 by 12 room?
A 12 by 12 room with 8 foot ceilings has about 384 square feet of wall area. One gallon covers about 350 to 400 square feet, so you need about one gallon for one coat. Two coats need two gallons. The calculator gives you the exact amount.
How much does it cost to paint a room?
A gallon of interior paint costs 30 to 60 dollars. A 12 by 12 room needs about one gallon per coat. Two coats of quality paint and supplies typically cost 100 to 200 dollars total. The calculator gives you the gallon count.
Do I need primer before painting?
Primer helps paint adhere and covers stains. Most new drywall benefits from a primer coat. Painting over a similar colour may not need primer. The calculator estimates paint volume, and you can double it if you need a separate primer coat.
How much paint for the ceiling?
The ceiling area equals the room length multiplied by width. A 12 by 12 room has 144 square feet of ceiling. One gallon covers that with some to spare. The calculator includes ceiling area in the estimate.
Should I paint the trim separately?
Yes, trim paint is usually a different type, often semi-gloss or high-gloss enamel. Calculate trim separately. The calculator can compute trim linear footage for you.
How many gallons of paint for a 12 by 14 room?
A 12 by 14 room with 8-foot walls has about 416 square feet of wall area. Subtract roughly 60 square feet for a door and two windows, leaving 356 paintable square feet. At 350 square feet per gallon and two coats, you need about 2 gallons. The calculator gives you the exact figure based on your dimensions, door and window count, and number of coats.