Paint Calculator

How to Measure a Room for Painting

Start by measuring the perimeter of the room — the total length of all four walls combined. Multiply that perimeter by the ceiling height to get your gross wall area. This is the maximum surface your paint could cover before subtracting openings.

A standard interior door is approximately 20 square feet (3 ft × 6.8 ft), and a standard window is approximately 15 square feet (3 ft × 5 ft). Subtract these from your gross area to get the net paintable surface.

For rooms with unusual features — archways, built-in shelving, fireplaces — subtract those surfaces from your total as well. The calculator above handles doors and windows automatically using standard size assumptions.

Understanding Paint Coverage

Most interior latex paints cover between 300 and 400 square feet per gallon on a smooth, properly primed surface. The default of 350 sq ft per gallon used in this calculator is a reliable middle-ground estimate.

Coverage decreases on rough or highly textured surfaces (brick, stucco, orange peel texture) because the paint must fill in the recesses. In these cases, use 250–300 sq ft per gallon as a more conservative estimate.

Darker colors and deep-toned paint may also require more product per coat to achieve full opacity. When in doubt, round up — it is always better to have a little leftover for touch-ups than to run short mid-wall.

When to Use More Coats

Two coats is the industry standard for most interior painting projects, and it is the default in this calculator. However, certain situations call for more:

• •Dramatic color changes. Going from dark to light (or vice versa) almost always requires an extra coat or a tinted primer coat first.
• •Previously unpainted drywall. New drywall is porous and absorbs the first coat heavily. Apply a dedicated primer, then two coats of finish paint.
• •High-traffic areas. Kitchens, bathrooms, and hallways benefit from three coats of a washable satin or semi-gloss finish for durability.

One coat is only suitable when you are using the same color over a sound, existing paint layer — often called a “refresh coat.”

Types of Paint and Finish

The finish (sheen level) of paint significantly affects how it looks, cleans, and holds up over time:

For most walls in living areas, eggshell is the go-to choice: it hides minor imperfections, is easy to clean, and has a subtle warmth that flat paint lacks.

Pro Tips for Painting a Room

• 1.
  Buy all your paint at once.Even the same color can vary slightly between batches (called “lots”). Buy enough for the entire project in one trip.
• 2.
  Prep is 80% of the job. Fill holes, sand rough spots, clean walls with TSP or a degreaser. Paint applied over a dirty or damaged surface will not adhere properly.
• 3.
  Use quality tools. A good roller cover and nylon-polyester brush apply paint more evenly and last for multiple projects. Cheap tools leave lint, streaks, and brush marks.
• 4.
  Cut in before rolling. Use a brush to paint a 2-inch border along all edges, corners, and trim, then roll the larger flat areas. Work in sections of one wall at a time to keep a wet edge.
• 5.
  Store leftover paint properly. Seal the can tightly (use the handle of a brush to press the lid down all around, then tap with a rubber mallet), label the color name and mix date, and store in a temperature-stable indoor area. Properly stored latex paint keeps for up to 10 years.

What Does Paint Actually Cost?

Interior paint prices vary widely by brand and quality tier. As a general guide:

Spending more on paint generally means better coverage, richer color, and more durable finish — especially important in high-traffic areas. The labor savings from needing one fewer coat of a premium paint can easily offset the price difference.