How Much Paint Do I Need?

The Simple Formula

The basic rule of thumb: one gallon (3.8L) of paint covers approximately 350–400 square feet (32–37 m²) of wall space with one coat. Most rooms need two coats, so double your estimate.

Step 1: Measure Your Walls

For each wall, multiply its width × height to get the area in square feet. Add all walls together for the total wall area.

• Measure each wall separately (width × height)
• Add all wall areas together
• Subtract doors (~21 sq ft each) and windows (~15 sq ft each)

Step 2: Account for Doors and Windows

A standard door is about 21 square feet and a typical window is about 15 square feet. Subtract these from your total — but only if you have more than 2 of each (small savings aren't worth the calculation complexity).

Step 3: Calculate by Room Type

Average Bedroom (12×12 ft, 8 ft ceiling)

• Wall area: ~384 sq ft
• Minus 1 door + 2 windows: ~384 − 51 = 333 sq ft
• For 2 coats: 333 × 2 = 666 sq ft ÷ 350 = ~1.9 gallons

Living Room (16×20 ft, 9 ft ceiling)

• Wall area: ~648 sq ft
• Minus doors/windows: ~580 sq ft
• For 2 coats: ~3.3 gallons → buy 4 gallons

Kitchen (10×12 ft, 9 ft ceiling)

• Wall area: ~396 sq ft
• Cabinets reduce paintable area significantly
• Typically need 1.5–2 gallons

Step 4: Don't Forget the Ceiling

Ceiling paint is typically applied in one coat using flat/matte paint. Calculate: room length × room width = ceiling area. A 12×12 room needs ~0.4 gallons.

Step 5: Trim, Doors & Baseboards

Trim paint is applied in smaller amounts. Budget 1 quart per 100 linear feet of trim. A typical room needs about 0.5–1 quart for all baseboards and door/window casings.

Tips to Avoid Waste

Use Our Free Paint Calculator

Skip the manual math — our free paint calculator does all of this instantly. Just enter your room dimensions and it tells you exactly how many litres or gallons you need.