How many gallons of paint do I need for a 12x12 room?

A 12×12 room with 8-foot ceilings has about 384 square feet of wall area. After subtracting one door and two windows (roughly 50 sq ft), you have 334 sq ft. At 350 sq ft per gallon, you need about 1 gallon per coat. For two coats, buy 2 gallons. Add a third if you're making a dramatic color change.

Do I need primer before painting?

Primer is essential when painting new drywall, bare wood, or after major repairs. It's also important when making a significant color change. On previously painted walls in good condition with a similar color, you can often skip primer and use two coats of quality paint instead.

How long does paint last once opened?

Sealed latex paint stored at room temperature lasts 2–5 years. Once opened, ensure you press the lid firmly shut and store it away from freezing temperatures. Stir paint thoroughly before each use. If paint has chunks or a sour smell, it has gone bad and should be disposed of properly.

How much paint do I need for exterior walls?

Measure the total wall area (perimeter × height) and subtract windows and doors. Exterior paint covers 250–350 sq ft per gallon on average siding. Budget for two coats and add 10% for waste. A 1,500 sq ft home exterior typically requires 10–15 gallons depending on siding texture.

Can I paint over dark colors without primer?

Painting light colors over dark without primer usually requires 3–4 coats of finish paint to fully cover the dark color. Using a gray or tinted primer reduces this to 2 coats. For the best results and most economical approach, apply one coat of tinted primer before your finish color.

How Much Paint Do You Need? Room-by-Room Guide

Paint Coverage: The Key Number

The most important number in any paint calculation is the coverage rate. One gallon of quality interior latex paint covers approximately 350–400 square feet of wall surface on a smooth, primed surface. On rough or porous surfaces, coverage drops to 250–300 square feet per gallon. Most manufacturers print the coverage rate on the label, so always check before purchasing.

How to Measure Your Walls

To calculate the total paintable wall area in a room, follow these steps:

Measure the perimeter of the room (add all four wall lengths together).
Multiply the perimeter by the ceiling height to get total wall area.
Subtract 20 square feet for each standard door (approximately 3×7 ft).
Subtract 15 square feet for each standard window (approximately 3×5 ft).
Divide the net area by 350 (or the coverage rate on your paint can) to get gallons needed per coat.
Multiply by the number of coats.

Example: A 12×14 foot room with 9-foot ceilings, 2 doors, and 2 windows: Perimeter = (12+14)×2 = 52 feet. Area = 52×9 = 468 sq ft. Subtract doors (40) and windows (30) = 398 sq ft. At 350 sq ft/gallon = 1.14 gallons per coat. Two coats = 2.28 gallons, so buy 3 gallons.

Two Coats: Always the Right Answer

Two coats of paint are standard for any quality paint job. Two coats provide better coverage, richer color, and longer-lasting durability than a single heavy coat. For dramatic color changes (going from white to dark red, or dark walls to light), a third coat may be necessary. When calculating, always multiply your one-coat total by 2 and round up to the nearest quart or gallon.

Do You Need Primer?

Primer creates a uniform base that improves paint adhesion and reduces the number of finish coats needed. You need primer when:

Painting over new drywall or bare wood
Making a dramatic color change (especially light over dark)
Painting over stains, water damage, or smoke damage
Painting a glossy surface

Primer typically covers 300–400 sq ft per gallon. Self-priming paints (paint + primer) can eliminate a separate primer coat for lighter color changes, but they are not a substitute for a dedicated primer on new drywall or major color shifts.

Choosing the Right Paint Sheen

Paint sheen affects both appearance and durability. Here's when to use each:

Flat/Matte: Best for ceilings and low-traffic walls. Hides imperfections well but difficult to clean.
Eggshell: The most popular choice for living rooms and bedrooms. Slight sheen, easier to clean than flat, good durability.
Satin: Good for hallways, kids' rooms, and moderate-traffic areas. Noticeably shiny, easy to wipe clean.
Semi-Gloss: Best for kitchens, bathrooms, trim, and doors. Highly moisture-resistant and very easy to clean.
Gloss: Used for trim, cabinets, and furniture where maximum durability is needed. Very shiny appearance.

Exterior Paint Calculations

For exterior painting, measure all wall surfaces including gable ends. Exterior paint typically covers 250–350 sq ft per gallon due to textured siding and absorption. Subtract window and door areas. Add 10–15% for trim and difficult-to-reach areas. Exterior paint also typically requires two coats for full weather protection.

How Much Paint Lasts in Storage

Unused latex paint sealed tightly and stored at room temperature lasts 2–5 years. Write the room name and mix color code on the can lid before storing — it's invaluable for touch-ups. Never freeze latex paint; freezing permanently ruins it. Oil-based paint lasts 5–10+ years in sealed cans.