Paint Calculator
Calculate paint needed for a room
Multiple surface types
Door/window deduction
Multiple coats
You're painting the living room. Four walls, two windows, one door. The paint can says "covers 350-400 sq ft per gallon." Do you need one gallon or three? Will one coat be enough, or should you plan for two?
Paint calculation prevents two common problems: buying too much and having expensive waste, or running out mid-project with color-matching headaches. This calculator tells you exactly what you need.
What is Paint Calculation?
Paint calculation determines how much paint is required to cover a surface area, accounting for coverage rate, number of coats, and openings (windows/doors). Different paint types and surface conditions affect coverage.
The formulas:
Wall area = (Length × Height × 4 walls) - Openings
Coverage per gallon: 350-400 sq ft (smooth wall, quality paint)
Coverage per gallon: 250-300 sq ft (textured/rough/dark base)
Gallons = Total Area ÷ Coverage Rate × Number of Coats
Even with quality paint and primer, two coats provides better coverage, durability, and color depth. Plan for it.
Why People Actually Need This Tool
Quality interior paint costs $40-80/gallon. Overbuying by two gallons wastes $100+. Underbuying means a second trip and potential color mismatch.
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Interior rooms — Calculate wall paint needs accurately.
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Exterior painting — Estimate siding and trim requirements.
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Ceiling coverage — Calculate separately from walls.
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Trim and doors — Smaller areas, different paint type.
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Budget estimation — Know total paint cost before starting.
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Color matching — Ensure enough paint from single batch.
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Commercial spaces — Large area calculations.
How to Use the Paint Calculator
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Enter room dimensions — Length, width, height.
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Enter openings — Number and size of windows/doors.
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Select surface type — Smooth, textured, previously painted.
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Select coats — One, two, or three coats.
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View results — Gallons needed with waste allowance.
| Surface Type | Coverage (sq ft/gal) | Notes |
|---|---|---|
| Smooth drywall | 350-400 | Best case scenario |
| Textured walls | 250-300 | Texture absorbs more paint |
| Bare drywall | 200-250 | Needs primer first |
| Dark to light | 250-300 | May need extra coats |
| Light to light | 350-400 | Standard coverage |
| Exterior wood | 300-350 | Varies by porosity |
| Exterior masonry | 150-200 | Very porous surface |
Bare surfaces need primer first. Primer at ~300 sq ft/gal, then paint. Some paints include primer but true primer is more economical.
Real-World Use Cases
1. The Living Room
Context: Room is 15' × 18' with 9' ceilings. Two windows (3' × 4'), one door.
Problem: How much paint for two coats?
Solution: Wall area: (15+18+15+18) × 9 = 594 sq ft - 30 sq ft openings = 564 sq ft. Two coats: 1128 sq ft ÷ 350 = 3.2 gallons.
Outcome: Buy 4 gallons for comfortable coverage.
2. The Accent Wall
Context: Single 12' × 10' wall getting bold color.
Problem: Paint needed for accent wall?
Solution: 120 sq ft × 2 coats = 240 sq ft. One quart covers ~100 sq ft. Need 3 quarts or 1 gallon.
Outcome: One gallon with some leftover for touch-ups.
3. The Exterior Project
Context: House exterior: 2,500 sq ft siding, plus 300 sq ft trim.
Problem: Total paint for exterior repaint?
Solution: Siding: 2500 ÷ 300 = 8.3 gal × 2 coats = 17 gallons. Trim: 300 ÷ 300 = 2 gallons.
Outcome: 17 gallons body color, 2 gallons trim color.
4. The Ceiling
Context: 14' × 16' room ceiling needs fresh coat.
Problem: Ceiling paint quantity?
Solution: 224 sq ft ÷ 400 (ceilings are smoother) = 0.56 gal × 2 coats = 1.12 gallons.
Outcome: 2 gallons ceiling paint (ceilings show roller marks—two coats essential).
5. The Dark Color Challenge
Context: Painting red accent wall, currently white.
Problem: How many coats for full red coverage?
Solution: Deep colors need 3+ coats OR tinted primer. 120 sq ft × 3 coats = 360 sq ft = 1+ gallons.
Outcome: Use gray-tinted primer first, then 2 coats red.
6. The Bathroom
Context: Small bathroom: 8' × 6' with 8' ceiling. Lots of tile, limited paintable area.
Problem: Account for tile and fixtures?
Solution: Gross: 224 sq ft walls - 80 sq ft tile/fixtures = 144 sq ft paintable × 2 = 288 sq ft.
Outcome: One gallon moisture-resistant paint is plenty.
7. The Touch-Up Reserve
Context: Completed painting, want to save touch-up paint.
Problem: How much to keep?
Solution: Keep 1 quart per room for touch-ups. Store properly—paint lasts 10+ years sealed.
Outcome: Future touch-ups perfectly color-matched.
Common Mistakes and How to Avoid Them
"400 sq ft coverage" assumes perfect conditions. Plan for 300-350 for realistic estimates.
Privacy and Data Handling
This Paint Calculator operates entirely in your browser.
- No calculations are sent to any server.
- No project data is stored.
- No account required.
- Works completely offline.
Your home improvement plans stay private.
Conclusion
Paint calculation saves money and trips to the store. Too little paint means project delays and color-matching nightmares. Too much means wasted money and storage hassles.
This calculator accounts for room dimensions, openings, surface types, and coat requirements. Know exactly what you need before you start.
Measure twice, buy once, paint beautifully.