How to Calculate How Much Paint You Need for Any Room

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

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.