Paint Calculator
Calculate exactly how much paint you need for your room. No more guessing or extra trips to the store.
Enter Room Details
Standard door = 20 sq ft
Standard window = 15 sq ft
How to Calculate Paint for a Room
Buying the right amount of paint saves money and ensures color consistency across your project. Here's everything you need to know about calculating paint quantities.
The Basic Formula
Gallons needed = (Wall area × Number of coats) ÷ 350 sq ft + 10%
One gallon of paint covers approximately 350-400 square feet. We use 350 sq ft for conservative estimates, then add 10% for waste, touch-ups, and surface variations.
Step-by-Step Calculation
- Measure walls: Calculate perimeter (length + width × 2) × height
- Subtract openings: Deduct 20 sq ft per door, 15 sq ft per window
- Multiply by coats: Most rooms need 2 coats
- Divide by coverage: 350 sq ft per gallon
- Add buffer: 10% extra for touch-ups and waste
- Round up: Always buy full gallons (you can't buy 1.3 gallons)
How Many Coats Do You Need?
| Situation | Coats Needed |
|---|---|
| Same color refresh | 1 coat (maybe) |
| Similar colors (white to off-white) | 1-2 coats |
| Different color (standard) | 2 coats (recommended) |
| Light over dark color | 2-3 coats + primer |
| Dark or bold colors (red, navy) | 3+ coats |
| New drywall | Primer + 2 coats |
Paint Sheen Guide
- Flat/Matte: Hides imperfections, best for ceilings and low-traffic areas
- Eggshell: Slight sheen, easy to clean, good for living rooms/bedrooms
- Satin: More sheen, very washable, ideal for hallways and family rooms
- Semi-Gloss: Durable and moisture-resistant, best for kitchens/bathrooms/trim
- Gloss: Highest durability, mainly for trim, doors, cabinets
Pro Tips for Better Results
- Buy from the same batch: Paint colors can vary slightly between batches. Check lot numbers.
- Stir, don't shake: Shaking creates bubbles. Stir thoroughly before and during painting.
- Use primer when needed: For new drywall, stains, or dramatic color changes.
- Don't cut it too close: Running out mid-wall creates visible seams. Buy extra.
- Store leftovers properly: Keep sealed paint for touch-ups. Mark cans with room names and dates.
Planning Your Paint Project
Before painting, it helps to have an accurate floor plan of your room. Use Room Sketch 3D to draw your room to scale, note where doors and windows are located, and export a plan with exact dimensions to reference during your project.
Frequently Asked Questions
How much paint do I need for a room?
One gallon of paint typically covers 350-400 square feet. Calculate your wall area (perimeter × height), subtract doors (20 sq ft each) and windows (15 sq ft each), then divide by 350. Our calculator does this automatically and accounts for the number of coats you need.
How many coats of paint do I need?
Most rooms need 2 coats for even coverage. Use 1 coat if painting the same color or using paint+primer. Use 3 coats when covering dark colors with light ones, or for bold/deep colors. Primer is recommended when painting new drywall or covering stains.
Should I buy extra paint?
Yes, buy 10-15% more than calculated for touch-ups and to account for surface porosity. Keep leftover paint (properly sealed) for future touch-ups. Our calculator includes this buffer in the recommendation.
Does paint sheen affect coverage?
Slightly. Flat/matte paints may need more coats to achieve even coverage compared to satin or semi-gloss. However, the square footage coverage per gallon is similar. Choose sheen based on the room's function: flat for ceilings, eggshell for living areas, semi-gloss for kitchens/baths.