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Paint Calculator
How many gallons of paint for your room? Enter the dimensions — we'll subtract doors and windows and add coats automatically.
Room measurements
Coverage: 1 gallon ≈ 350 sq ft per coat · door ≈ 21 sq ft · window ≈ 15 sq ft.
How to calculate paint by hand
- Wall area = 2 × (length + width) × ceiling height.
- Subtract 21 sq ft per door and 15 sq ft per window.
- Multiply by the number of coats, then divide by 350 (sq ft per gallon). Round up.
Example: 12×12 room, 8 ft ceilings, 2 coats → walls ≈ 384 sq ft − 36 (door+window) = 348 → ×2 coats = 696 → ÷350 = 2 gallons.
Paint FAQs
How many square feet does a gallon of paint cover?
About 350 sq ft per coat on smooth interior walls. Textured or unpainted surfaces can drop that to ~250 sq ft.
Is one coat of paint enough?
Rarely. Two coats give even color, better durability and true coverage — pros almost always apply two.
How much paint do I need for a ceiling?
Ceiling area = length × width. A 12×12 ceiling is 144 sq ft — about half a gallon per coat, so buy 1 gallon for two coats.
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Frequently asked questions
How much area does one gallon of paint cover?
One gallon of interior paint covers roughly 350 to 400 square feet with a single coat. Rough or textured walls absorb more, so coverage drops.
How many coats of paint should I apply?
Two coats is the standard for even color and durability. Going from dark to light colors may need a primer plus two coats.
Should I subtract doors and windows from wall area?
Yes. Measure each door at about 21 square feet and each window at about 15 square feet, then subtract them from the total wall area for an accurate gallon count.
How much extra paint should I buy?
Buy about 10 percent extra for touch-ups and future repairs. Leftover paint stored sealed lasts for years.