What is the Paint Coverage Calculator?
The Paint Coverage Calculator helps homeowners and professional painters mathematically determine how many gallons of primer and paint are required to coat a wall. It subtracts the dead space of doors and windows, ensuring you buy the perfect amount of paint without expensive waste.
How to Calculate Gallons of Paint Needed (Formulas)
Most high-quality interior latex paints cover roughly 350 square feet per gallon on smooth drywall.
- Total Wall Area: Wall Width * Ceiling Height.
- Deduct Openings: Subtract 21 sq ft for every standard door, and 15 sq ft for every standard window.
- Total Gallons Formula: (Total Wall Area - Openings Area) / 350.
- Multiply by 2 if applying the mandatory second coat!
Frequently Asked Questions
Can I get away with just one coat of paint?
Almost never. Even "premium one-coat" paints marketed heavily at big box stores require two coats for a flawless finish. The first coat seals the drywall and establishes the base, while the second coat provides the true, saturated color depth, hides roller streaks, and creates a durable, washable surface.
Do I need to buy primer?
If you are painting over brand new, bare drywall, you absolutely must use a dedicated PVA drywall primer first to seal the porous paper. If you are painting a light color over a dark, harsh color (like painting yellow over dark navy blue), a high-hide grey primer is mandatory. If you are just refreshing a white wall, primer is not needed.
How much extra paint should I keep for touch-ups?
It is standard practice to save roughly 1 quart of the leftover paint in a tightly sealed, cool, dark place. This ensures you have the exact, perfectly color-matched dye lot available to touch up scuffs, scratches, or holes caused by moving furniture years down the road.