Paint Gallons Calculator
Determine exactly how many gallons of paint you need to buy for your walls. Adjust room sizes, ceilings, window cutouts, doors, and coats.
Estimated Paint Needed
0 Gallons
Net Wall Area: 0 sq ft
How Much Paint Do I Need?
A standard rule of thumb is that **one gallon of paint covers approximately 350 to 400 square feet** of smooth wall surface with a single coat. However, you should always plan for two coats to get an even, professional finish that covers completely.
How to Calculate Wall Square Footage manually
To calculate how many gallons of paint you need to buy:
- Find Wall Perimeter: Add the length of all four walls together. For example, a 10x12 room has a perimeter of 10 + 10 + 12 + 12 = 44 feet.
- Find Gross Wall Area: Multiply the perimeter by the ceiling height. If the ceiling is 8 feet high, gross wall area is 44 × 8 = 352 square feet.
- Subtract Cutouts: Subtract 20 square feet for each standard door and 15 square feet for each window. 1 door and 1 window equals 35 square feet of deduction. Net Area = 352 - 35 = 317 square feet.
- Account for Coats: Multiply the net area by the number of coats (typically 2). 317 × 2 = 634 square feet of coverage needed.
- Calculate Gallons: Divide the total coverage area by 350. 634 / 350 = 1.81 gallons. You would need to buy 2 full gallons of paint.
Frequently Asked Questions
One coat is rarely enough unless you are applying the exact same color and brand to touch up minor scuffs. A second coat ensures true color depth, covers roller overlaps, and seals minor porous spots.
There are four quarts in a gallon. One quart covers approximately 90 to 100 square feet of wall space with a single coat, making it ideal for painting accent trim, moldings, or small closet areas.