Paint Coverage Calculator

Stop overbuying paint. Enter room dimensions, doors, windows, and coats to see exactly how many gallons (and quarts for touch-up) you need. Adjust coverage to match your specific paint, and estimate cost with your gallon price.

How This Calculator Works

The calculator measures paintable wall surface, then divides by coverage. Wall area is the room perimeter, 2 × (length + width), times the ceiling height. It subtracts about 20 sq ft per door and 15 sq ft per window so you are not buying paint for openings. If you are painting the ceiling, length × width is added. That paintable area is multiplied by the number of coats — two coats doubles the surface you actually cover.

Gallons are the coated area divided by your coverage rate, defaulting to 350 sq ft per gallon, which is realistic for a quality interior latex on primed drywall. The result is reported to the hundredth of a gallon, plus a quart count for touch-ups, and cost is based on rounding up to whole gallons times your price per gallon, since the store sells full cans.

A Worked Example

A 14×16 ft living room, 9 ft ceilings, three windows and one door, two coats, walls only. Perimeter: 2 × (14 + 16) = 60 ft; wall area 60 × 9 = 540 sq ft. Subtract 1 door (20) and 3 windows (45) = 65, leaving 475 sq ft. Two coats: 950 sq ft of coverage. At 350 sq ft/gallon that is 2.71 gallons, so you buy 3 gallons. At a 2026 premium-paint price near $52/gallon, that is $156 plus a quart on the shelf for touch-ups.

Estimator's tip: Buy your wall color in one batch and have the store box (intermix) the gallons if you bought several — can-to-can tint can vary just enough to flash on a long wall in side light. Round up to the next full gallon even when the math says 2.7; the spare quart you keep sealed is your touch-up paint two years from now, and a re-tinted “match” rarely disappears on the wall.

What Affects Your Paint Quantity

• Number of coats — dark over light or new drywall almost always needs two.
• Coverage rate, which drops on porous, textured, or unprimed surfaces.
• Surface texture: knockdown and orange-peel walls drink more than smooth ones.
• Color change — deep accent colors and red bases often need an extra coat or tinted primer.
• Doors and windows you deduct, and whether trim and ceiling are included.
• Paint quality; cheaper paint covers less per gallon and often needs the extra coat anyway.

Frequently Asked Questions

How much paint do I need for a room?

Find wall area (perimeter times height), subtract doors and windows, multiply by coats, then divide by 350 square feet per gallon. An average 12x12 room takes about 1.5 gallons for two coats.

How many square feet does a gallon of paint cover?

A gallon covers roughly 350 to 400 square feet in one coat on smooth, primed drywall. Textured, porous, or new surfaces pull that down toward 250 to 300, so use the lower end if in doubt.

Do I need one coat or two?

Most jobs need two coats for even color and durability, especially over new drywall, when changing colors, or with deep tints. One coat may suffice when repainting the same light color over a clean, primed wall.

Should I include the ceiling in my paint estimate?

Only if you are painting it. The calculator adds length times width for the ceiling when you check that box; ceilings usually use a dedicated flat ceiling paint rather than the wall color.