How to Calculate How Much Paint You Need
Buying the right amount of paint prevents both costly waste and frustrating mid-project trips back to the store. Most interior paints cover 350–400 square feet per gallon on a smooth surface; textured or porous surfaces may need 300 sq ft/gallon or less.
Step-by-Step Calculation
Step 1: Calculate total wall area Measure each wall's width and height, then multiply. For a 12 × 14 ft room with 8 ft ceilings:
- Two 12 ft walls: 2 × (12 × 8) = 192 sq ft
- Two 14 ft walls: 2 × (14 × 8) = 224 sq ft
- Total wall area: 416 sq ft
Step 2: Subtract doors and windows
- Average door: 20 sq ft
- Average window: 15 sq ft
- Subtract: 416 − 20 − 15 = 381 sq ft
Step 3: Calculate gallons needed Using 350 sq ft/gallon coverage: 381 / 350 = 1.09 gallons → Round up to 2 gallons (for two coats)
For two coats: 1.09 × 2 = 2.18 → Buy 3 gallons (keep the extra for touch-ups)
Ceiling Paint
Calculate ceiling area separately: 12 × 14 = 168 sq ft → 1 gallon (one coat usually sufficient)
Coverage Rates Reference
| Surface | Coverage (sq ft/gallon) |
|---|---|
| Smooth drywall | 400 |
| Previously painted | 350–400 |
| Fresh drywall primer | 300–350 |
| Textured or brick | 250–300 |
| Bare wood | 300–350 |
Primer Rule
If painting a new color significantly different from the current color (especially going from dark to light), use a primer first. One coat of primer counts as one coat of paint coverage.
Use our paint calculator to get exact quantities for any room.