Paint Calculator

How to Calculate Paint for a Room

Buying the right amount of paint saves money and avoids extra trips to the store. Whether you are painting a single accent wall or an entire house, this paint calculator gives you an accurate estimate of the gallons you need. The calculation accounts for doors, windows, and the number of coats to provide a practical, real-world result.

The Paint Calculation Formula

Our paint calculator follows the standard method used by professional painters:

1. Calculate total wall area: 2 × (Length + Width) × Height = total wall square footage.
2. Subtract doors: Each standard door is approximately 21 sq ft (3 ft × 7 ft).
3. Subtract windows: Each standard window is approximately 15 sq ft (3 ft × 5 ft).
4. Multiply by coats: Paintable area × number of coats = total coverage needed.
5. Divide by coverage rate: Total coverage ÷ 350 sq ft per gallon = gallons of paint needed.

Paint Coverage by Type

Different paint types have slightly different coverage rates:

• Flat / Matte: 350–400 sq ft per gallon. Best for ceilings and low-traffic rooms.
• Eggshell: 350–400 sq ft per gallon. Popular for living rooms and bedrooms.
• Satin: 350–400 sq ft per gallon. Good for kitchens, bathrooms, and hallways.
• Semi-gloss: 350–400 sq ft per gallon. Ideal for trim, doors, and cabinets.
• High-gloss: 300–350 sq ft per gallon. Used for accents, furniture, and high-moisture areas.

When to Use More Coats

Two coats is the standard recommendation for most painting projects, but some situations call for more:

• Dark over light (or light over dark): Dramatic color changes often need 2–3 coats, even with primer.
• Red, yellow, and orange paints: These colors have lower pigment density and may require 3 coats for even coverage.
• Bare drywall or new plaster: Unpainted surfaces are porous and absorb the first coat. Use a primer plus 2 coats of paint.
• Textured walls: Rough surfaces like stucco or popcorn walls require more paint per coat and may need an extra coat for full coverage.

Gallons vs. Quarts: What to Buy

A quart of paint covers approximately 87 square feet (one-quarter of a gallon). Buy quarts when you need less than one gallon — small bathrooms, accent walls, or touch-up projects. For anything larger, gallons are more economical, typically saving 20–30% per square foot compared to quart pricing. Most paint retailers offer 5-gallon buckets at an additional discount for large projects like whole-house painting.

Paint Estimating Tips from the Pros

• Buy 10% extra: Always round up and buy a little more than calculated to account for waste, touch-ups, and roller absorption.
• Keep leftovers: Store unused paint for future touch-ups. Label the can with the room name and date.
• Prime first: Using primer reduces the amount of finish paint needed, especially on new drywall, stains, or drastic color changes.
• Measure twice: Accurate measurements save money. Measure each wall individually for irregular rooms.
• Test before committing: Buy a sample size to test color on the wall before purchasing full gallons. Colors look different under various lighting conditions.

Common Room Sizes and Paint Estimates

For quick reference with 8-foot ceilings, 1 door, and 2 windows at 2 coats:

• 10 × 10 room: ~1.5 gallons
• 12 × 12 room: ~2 gallons
• 12 × 15 room: ~2.5 gallons
• 15 × 20 room: ~3.5 gallons
• 20 × 20 room: ~4 gallons