Paint Calculator
### Home Renovation & Wall Paint Estimation Painting interior walls requires calculating **Net Paintable Surface Area**, which accounts for wall height and length while deducting unpainted.
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📐 Formula
💡 Practical Example
Estimating paint for a 20' x 15' living room with 9' ceilings, 2 doors (42 sq ft deduction), 3 windows (36 sq ft deduction), and 2 coats of latex paint: Requires 3.15 exact gallons and purchasing 4 gallon cans.
📖 About Paint Calculator
Home Renovation & Wall Paint Estimation
Painting interior walls requires calculating Net Paintable Surface Area, which accounts for wall height and length while deducting unpainted architectural features like doors, windows, fireplaces, and built-in shelving.
Core Paint Equations
- Room Perimeter: Perimeter = 2 ×
- Gross Wall Area: Gross Area = Perimeter × Ceiling Height
- Standard Deductions: Door Deduction = 21 sq ft, Window Deduction = 12 sq ft
- Net Area: Net Area = Gross Area - (Doors × 21) - (Windows × 12)
- Gallons Needed: Gallons = Net Area × CoatsCoverage Rate
Industry Coverage Standards per Gallon
- Smooth Drywall / Plaster: 350 to 400 sq ft per gallon.
- Rough Textured Drywall / Masonry: 250 to 300 sq ft per gallon.
- Unprimed Bare Wood: 200 to 250 sq ft per gallon (requires primer coat).
How to Use This Calculator
Enter your Room Length (e.g. 20 in ft), Room Width (e.g. 15 in ft), Ceiling Height (e.g. 9 in ft), Number of Doors (e.g. 2 in doors), Number of Windows (e.g. 3 in windows), Number of Paint Coats — choose from 1 Coat (Touch-up / Prime Coat), 2 Coats (Standard Full Coverage), 3 Coats (Deep Color Change), and Paint Coverage Rate (e.g. 350 in sq ft/gal). Measure twice before entering dimensions — small measurement errors scale up significantly in material estimates.
The Formula
Perimeter = 2 * (length + width)
Gross Wall Area = Perimeter * Height
Total Area to Paint = Net Area * Coats
Worked Example
Estimating paint for a 20' x 15' living room with 9' ceilings, 2 doors (42 sq ft deduction), 3 windows (36 sq ft deduction), and 2 coats of latex paint: Requires 3.15 exact gallons and purchasing 4 gallon cans.
Understanding Your Result
Standard interior latex paint covers 350–400 sq ft per gallon for a single coat on smooth surfaces; add 20–25% for textured or porous surfaces. Two-coat applications are standard for full color changes; deep colors may need three coats. Subtract 20 sq ft per standard door and 15 sq ft per window. Paint quantities round up to the nearest full gallon — partial gallons are not returnable at most retailers.
💡 Methodological Standards & Calculation Accuracy
- All calculations are performed client-side in your browser using verified, standards-compliant mathematical algorithms.
- Results are provided for educational and informational analysis; verify critical applications with certified domain specialists.
- Ensure input values are entered in consistent units matching the selector options to guarantee accurate outputs.
- Periodic recalibration is recommended whenever baseline assumptions, operating parameters, or external conditions change.
Results are for informational and educational purposes only. Always verify critical decisions with a qualified professional.