How Much Paint Do I Need? A Room-by-Room Guide

The Coverage Rule

One gallon of paint covers approximately 350 square feet on a smooth surface with one coat. Textured walls (knockdown, orange peel, popcorn) reduce this to 250-300 square feet because the texture creates more surface area. Bare drywall that hasn't been primed soaks up paint and reduces coverage to about 200 square feet per gallon on the first coat.

This 350 number is the starting point for all paint calculations. Everything else is just figuring out how many square feet of surface you're painting.

Calculating Wall Area

Measure the perimeter of the room (length + width + length + width) and multiply by the ceiling height. A 15x12 room with 8-foot ceilings: perimeter = 54 feet, times 8 = 432 square feet of wall area.

Then subtract for openings. A standard interior door is about 21 square feet. A standard window is about 15 square feet. Two doors and two windows in our example room: 432 - (2 x 21) - (2 x 15) = 360 square feet of paintable wall area.

Two Coats: Not Optional

One coat looks fine from 10 feet away and terrible up close. Two coats provide even coverage, consistent color, and proper hide (the ability of paint to cover what's underneath). The only time one coat works is touch-ups with the exact same paint or recoating with the exact same color.

When changing colors, especially from dark to light, you may need three coats or a tinted primer. Going from dark red to white without primer is a five-coat nightmare. A gray-tinted primer reduces the topcoat to two coats every time.

Choosing a Finish

Flat finish hides wall imperfections best and is standard for ceilings and low-traffic rooms. It scuffs and stains easily and is difficult to clean. Eggshell is the most popular wall finish: slight sheen, hides imperfections reasonably well, and can be wiped clean. It works for living rooms, bedrooms, and hallways. Satin has more sheen and cleans easily, making it ideal for kitchens, bathrooms, kids' rooms, and hallways. Semi-gloss is for trim, doors, cabinets, and high-moisture areas. It's the most durable and easiest to clean but shows every wall imperfection.

Primer: When You Need It

New (unpainted) drywall always needs primer. Stains from water, smoke, or markers need stain-blocking primer (shellac-based for worst cases). Dramatic color changes need tinted primer. Previously painted walls in good condition being repainted a similar color usually don't need primer since modern paint-and-primer-in-one products handle this adequately.

The Prep Nobody Wants to Do

Prep is 80% of a professional-looking paint job. Fill nail holes and dings with lightweight spackle, sand smooth after drying, and wipe dust. Remove outlet and switch covers (takes 30 seconds each and looks infinitely better than trying to cut around them). Tape edges with quality painter's tape (the blue 3M tape is worth the premium over cheap masking tape). Lay drop cloths on floors. Clean walls with a damp cloth or TSP solution to remove grease and dust.

Skipping prep shows in the final result every time. The actual painting goes faster than the prep, but nobody brags about how fast they taped the edges.