Paint Calculator

Estimate how much paint you need for walls, ceilings, and trim. This tool processes all data locally in your browser. No information is ever sent to any server. Completely free, no registration required.

How to Use the Paint Calculator

1. Enter your input values above
2. Results update automatically
3. Copy or download the output

What is a Paint Calculator?

A Paint Calculator estimates how many gallons of paint you need for any room based on wall dimensions, ceiling height, number of doors and windows, and paint coverage rate. The most common DIY mistake is buying too much or too little paint — too much wastes money (~$30-60/gallon for quality paint), too little means an extra trip to the store mid-project (and potential color-matching inconsistencies between batches). This calculator accounts for multiple coats, different paint types (primer, ceiling, wall, trim), and the coverage differences between flat, eggshell, satin, and semi-gloss paints.

How Does It Work?

Enter room dimensions: length, width, ceiling height. Add doors and windows (standard sizes pre-filled: door ≈ 20 sq ft, window ≈ 15 sq ft — or enter custom dimensions). Enter the number of coats (2 coats is standard for color changes; 1 for repainting the same color). The calculator computes: Total Wall Area = 2 × (Length + Width) × Height − Door Area − Window Area; Gallons = (Total Area × Coats) ÷ Coverage Rate (typically 350-400 sq ft per gallon). It shows gallons needed rounded up to the next quart (1/4 gallon).

Formula

Wall Surface Area = 2 × (L + W) × H\nCeiling Area = L × W\n\nTotal Paintable Area = Walls + Ceiling − Doors − Windows\n\nPaint Needed (gallons) = (Total Area × Number of Coats) ÷ Coverage Rate\n\nCoverage Rates:\n• Flat/Matte: 350-400 sq ft/gallon\n• Eggshell/Satin: 300-350 sq ft/gallon\n• Semi-Gloss (trim/doors): 250-300 sq ft/gallon\n• Primer (new drywall): 200-300 sq ft/gallon\n\nStandard Deductions:\n• Interior Door: ~20 sq ft\n• Window: ~15 sq ft\n• Closet Door: ~21 sq ft (bi-fold)

Who Uses This Tool?

• DIY homeowners planning interior paint projects
• Contractors estimating paint quantities for quotes
• Home renovators budgeting for whole-house repainting
• Real estate agents estimating costs to freshen a listing
• First-time painters unsure how much to buy

Pro Tips

• Always buy paint by the gallon for large areas — it's cheaper per ounce than quarts. One gallon covers one average room (12×12 with 8ft ceiling) with one coat
• Buy all paint at once and ask the store to shake all gallons together — even computer-matched paint can have slight batch-to-batch color variation
• Primer dramatically reduces paint needed on new drywall or when covering dark colors. Budget 1 coat primer + 2 coats paint for color changes
• The coverage on the can (350-400 sq ft) assumes smooth, primed walls. Textured, porous, or unpainted surfaces may cut coverage by 25-50%. Buy 10-20% extra for touch-ups later

Frequently Asked Questions about Paint Calculator

How many coats of paint do I need?

Same color refresh: 1 coat. Color change (light→dark or dark→light): 2 coats minimum (sometimes 3 for extreme changes like white over red). New drywall: 1 coat primer + 2 coats paint. Going from dark to white: definitely budget 2-3 coats plus primer.

Should I buy paint by the gallon or 5-gallon bucket?

For one room: gallon. For multiple rooms or a whole-house project: 5-gallon buckets are 15-25% cheaper per gallon. But make sure you'll use it — opened paint lasts ~2-5 years if sealed properly.

Free online Paint Calculator — no signup, 100% client-side processing. All data stays in your browser.