Buying too much paint wastes money. Buying too little means a second trip to the store — and hoping the new batch matches your original color. Here's how to calculate exactly how much paint you need.
The Basic Paint Formula
One gallon of paint covers approximately 350–400 square feet with one coat. For two coats (which is standard), plan on one gallon per 175–200 square feet of wall area.
How to Calculate Wall Area
- Add up the total perimeter of the room (all wall lengths combined)
- Multiply perimeter by ceiling height to get total wall area
- Subtract door area (approximately 21 sq ft per door)
- Subtract window area (approximately 15 sq ft per window)
- Divide by 350 for one coat, or 175 for two coats
Example: Standard 12×14 Bedroom
- Perimeter: (12+14) × 2 = 52 linear feet
- Wall area: 52 × 9 ft ceiling = 468 sq ft
- Minus 1 door and 2 windows: 468 - 21 - 30 = 417 sq ft
- For 2 coats: 417 ÷ 175 = 2.4 gallons → buy 3 gallons
| Room Size | Paint Needed (2 coats) |
|---|---|
| Small bedroom (10×10) | 1–2 gallons |
| Standard bedroom (12×14) | 2–3 gallons |
| Living room (16×20) | 3–4 gallons |
| Open plan (20×30) | 5–6 gallons |
Pro Tip: Always buy a little extra and store it for touch-ups. Even the same brand and color can vary slightly between batches. Label the can with the room name.
Ceiling and Trim Paint
Ceiling paint: calculate ceiling square footage (length × width). One gallon covers about 400 sq ft. Most ceilings only need one coat of white ceiling paint.
Trim paint: calculate the linear footage of all trim, doors, and window casings. A quart of trim paint covers about 100 linear feet.
Calculate Your Paint Needs Instantly
Enter your room dimensions and get exact gallons needed for walls, ceiling, and trim.
Use Paint Calculator →Choosing the Right Paint Finish
- Flat/Matte — Best for ceilings and low-traffic walls. Hides imperfections.
- Eggshell — Great for living rooms and bedrooms. Easy to clean.
- Satin — Best for kitchens, bathrooms, and hallways. Moisture resistant.
- Semi-gloss — Ideal for trim, doors, and cabinets. Very durable.