Interior & Exterior Paint Coverage & Gallons Calculator
### Home Improvement & Painting: Estimating Surface Coverage 1. **The 350–400 Sq Ft Rule**: One standard US gallon of quality architectural interior latex paint covers approximately 350 to 400.
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📐 Formula
💡 Practical Example
For example, painting a \(16' \times 12'\text{ bedroom with } 9'\text{ ceilings}\)) with \(2\text{ doors (40 sq ft)}\) and \(3\text{ windows (45 sq ft)}\) applying \(2\text{ coats}\) of paint at \): Net paintable wall area is \. Total 2-coat coverage is \(838\text{ sq ft}\) (\(2.39\text{ exact gallons}\)). Purchase \(\mathbf{3\text{ Gallons of paint (\$135.00)}}\) with adequate margin for roller naps and touch-ups.
📖 About Interior & Exterior Paint Coverage & Gallons Calculator
Home Improvement & Painting: Estimating Surface Coverage
- The 350–400 Sq Ft Rule: One standard US gallon of quality architectural interior latex paint covers approximately 350 to 400 square feet on smooth, primed drywall.
- The 10% Wastage Buffer: Professional painters always purchase 10% extra volume to account for roller cage absorption, cut-in brush retention, and future wall touch-ups.
How to Use This Calculator
Enter your Room Length (Feet [ft]) (e.g. 16), Room Width (Feet [ft]) (e.g. 12), Ceiling Height (Feet [ft]) (e.g. 9 (8, 9, or 10 ft standard)), Number of Standard Doors (20 sq ft each) (e.g. 2), Number of Standard Windows (15 sq ft each) (e.g. 3), Number of Paint Coats — choose from 1 Coat (Same color refresh / primer already applied), 2 Coats (Standard quality full coverage), 3 Coats (Dark-to-light color transformation / raw drywall), Paint Coverage Spread Rate (sq ft / Gallon) (e.g. 350 (350–400 sq ft/gal standard)), and Paint Price per Gallon ( / gal) (e.g. 45 (45/gal premium latex)). Measure twice before entering dimensions — small measurement errors scale up significantly in material estimates.
The Formula
Paint Coverage equations:
Perimeter = 2 × (Length + Width)
Gross Wall Area = Perimeter × Ceiling Height
Deductions = (Doors × 20 sq ft) + (Windows × 15 sq ft)
Net Paintable Area = Gross Wall Area - Deductions
Gallons to Buy = ((Net Area × Coats) / (Coverage Rate (sq ft/gal))) × 1.10
Worked Example
For example, painting a 16' × 12' bedroom with 9' ceilings) with 2 doors (40 sq ft) and 3 windows (45 sq ft) applying 2 coats of paint at : Net paintable wall area is . Total 2-coat coverage is 838 sq ft (2.39 exact gallons). Purchase 3 Gallons of paint (\135.00) with adequate margin for roller naps and touch-ups.
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.