📖 Overview
Enter your room size and coverage rate to estimate the gallons of paint needed for your project.
🧪 Example Scenarios
Use these default and higher-pressure example inputs to explore how sensitive this calculator is before using your real numbers.
| Input | Base Case | Higher Pressure Case |
|---|---|---|
| Room Length (ft) | 12 | 13.8 |
| Room Width (ft) | 10 | 11.5 |
| Wall Height (ft) | 9 | 10.35 |
| Paint Coverage (sq ft/gallon) | 350 | 402.5 |
⚙️ How It Works
Calculates total paintable wall area from room dimensions, then divides by the coverage rate per gallon to determine how much paint to buy.
The Formula
Wall Area = 2 × (Length + Width) × Height | Gallons = Wall Area ÷ Coverage per Gallon
| Length, Width | Room floor dimensions in feet |
| Height | Ceiling height in feet (US standard: 8–9 ft) |
| Coverage | Sq ft per gallon (350 for smooth walls; 250–300 for textured) |
💡This formula calculates all four walls but does NOT subtract windows and doors. A rough rule of thumb: subtract 20 sq ft per standard door and 15 sq ft per window. For two coats, double your gallon estimate.
Quick Reference
| Room size | Wall area (8 ft ceiling) | Gallons needed (350 sq ft/gal) |
|---|---|---|
| 10 × 10 | 320 sq ft | ~0.9 gal |
| 12 × 12 | 384 sq ft | ~1.1 gal |
| 14 × 16 | 480 sq ft | ~1.4 gal |
| 20 × 20 | 640 sq ft | ~1.8 gal |
When To Use This
- Use this tool when you need a fast decision during active planning or execution.
- Use this before committing money, time, or tradeoffs that are hard to reverse.
- Use this to compare options using the same assumptions across scenarios.
Edge Cases To Watch
- Results can be misleading if key inputs are missing, stale, or unrealistic.
- Very small or very large values may amplify rounding effects and interpretation risk.
- If assumptions change mid-decision, recalculate before acting.
Practical Tips
💡 Add 10–15% extra for touch-ups and wastage.
💡 Textured or rough surfaces absorb more paint — use 250 sq ft/gallon instead of 350.
💡 Two coats nearly always look better; plan for double the quantity.
💡 Measure twice — a 12×14 room has 40% more wall area than a 10×10.
Frequently Asked Questions
❓ Does this include the ceiling?
No. The formula covers the four walls only. Add ceiling area (length × width) separately.
❓ What coverage rate should I use?
350 sq ft/gal for smooth drywall, 250–300 for textured or previously unprimed surfaces.