Paint Coverage per Gallon: How to Estimate Walls, Coats, and Waste
October 21, 2026
One gallon of paint typically covers 350 to 400 square feet on a smooth surface, with one coat. To estimate a room, find the wall area, subtract openings, multiply by the number of coats, and divide by coverage. A 12 × 14 ft room with 8 ft walls has 416 square feet of wall; after a door and two windows are removed, about 365 remain, and two coats need about 2.1 gallons.
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Wall area = perimeter × height. For a 12 × 14 ft room: perimeter = 2 × (12 + 14) = 52 ft, and 52 × 8 = 416 square feet. A standard door is about 21 square feet (3 × 7 ft) and a typical window about 15 square feet. Subtracting one door and two windows leaves 416 − 21 − 30 = 365 square feet.
Two coats require 730 square feet of coverage. At 350 square feet per gallon, you need 2.09 gallons, so buy 2 gallons plus a quart, or simply a third gallon for touch-ups.
What Changes Coverage
Coverage printed on the can assumes smooth, primed walls. Rough textures, such as stucco or heavy orange peel, can reduce coverage by 20% to 30%. Bare drywall and patched areas absorb more paint on the first coat.
Going from a dark color to a light one, or the reverse, usually needs a primer or an additional coat. Tinted primer can reduce the number of finish coats required.
- Smooth primed walls: 350 to 400 sq ft per gallon.
- Rough or porous surfaces: 250 to 300 sq ft per gallon.
- Bare drywall: prime first or expect heavy absorption.
- Dramatic color change: plan for primer plus two coats.
Ceilings, Trim, and Waste
Ceilings are calculated as length × width: 12 × 14 = 168 square feet, which fits within one gallon for one coat. Trim and doors use much less paint, typically a quart covers trim for a medium room.
Keep a little leftover paint for touch-ups, labelled with the room and date. Buying slightly more from a single batch also avoids slight color differences between cans.
Frequently Asked Questions
How much paint do I need for a 12x14 room?
With 8 ft walls and two coats, about 2 gallons for the walls after subtracting a door and two windows.
How many square feet does a gallon of paint cover?
Usually 350 to 400 square feet for one coat on smooth surfaces.
Do I need to subtract windows and doors?
It is optional but saves paint. Many people subtract only large openings and ignore small ones as a built-in allowance for waste.
Should I use primer?
Use primer on bare drywall, stained areas, or when changing color drastically. It improves coverage and finish.