How to Use the Paint & Primer Calculator
Painting a room is one of the most rewarding weekend DIY projects, but buying the wrong amount of paint is a common headache. Buying too little means a frustrating mid-project run to the hardware store (and hoping the color mixed matches perfectly), while buying too much means wasting money on cans that will sit in your garage for a decade.
Our free Paint & Primer Calculator takes the guesswork out of the paint aisle. By simply entering your wall dimensions and the number of doors and windows, this tool calculates exactly how many gallons you need to buy.
The Paint Math: How it Works
The industry standard is that 1 gallon of paint covers approximately 350 to 400 square feet of smooth wall surface (one coat). To figure out your needs, you must calculate the total square footage of your walls and subtract the areas you won't be painting.
Our calculator automatically deducts 20 square feet for every standard door and 15 square feet for every standard window. (Total Wall Length × Ceiling Height) - (Doors × 20) - (Windows × 15) = Net Square Footage
How Many Coats Do You Need?
Even if you buy "one-coat" premium paint, professionals always recommend applying at least two coats for a uniform, durable finish.
- 1 Coat: Only recommended if you are repainting a wall with the exact same color just to freshen it up.
- 2 Coats (Standard): The golden rule for almost all painting projects. It provides full coverage and brings out the true richness of the color.
- 3 Coats: Necessary when painting over a very dark color with a much lighter color, or when painting over heavily textured walls.
Do You Actually Need Primer?
Many modern paints are "Paint + Primer" in one. However, you should buy dedicated primer if you are painting over raw drywall, painting over oil-based paint with latex paint, or trying to cover up heavy stains, smoke damage, or very dark colors.