Paint Calculator
Enter your room's dimensions to find out how many gallons of paint or rolls of wallpaper you need, rounded up to a practical amount you can actually buy.
Last updated
How much paint do I actually need?
Most interior paint covers roughly 350 square feet per gallon for a single coat, though this varies a bit by brand and wall texture. To estimate your room, this calculator multiplies the room's perimeter by the wall height to get total wall area, then subtracts a standard allowance for each door (about 20 square feet) and window (about 15 square feet) you enter. Two coats matters more than people expect: a single coat rarely gives even, opaque coverage, especially over a darker existing color, so most painters plan for two coats as the default rather than the exception. Wallpaper works on the same total-area logic, just divided by how much a standard roll covers instead of a gallon.
Here's the math worked out for a typical bedroom, 14 feet by 12 feet with 8 foot walls, one door, and two windows. The perimeter is 2 times (14 plus 12), or 52 feet, and multiplying by the 8 foot ceiling height gives 416 square feet of gross wall area. Subtracting one door (20 sq ft) and two windows (30 sq ft total) leaves 366 square feet of actual wall to paint. At two coats, that's 732 total square feet of coverage needed. Dividing by 350 sq ft per gallon gives 2.09 gallons, which the calculator rounds up to the nearest quart (2.25 gallons) and then up again to a full 3 gallons, since paint is sold by the can, not by the exact fraction. For wallpaper on that same 366 square foot wall, dividing by the standard 30 sq ft per roll (after allowing for trim waste) rounds up to 13 rolls.
Coverage figures reflect commonly cited paint-industry averages, always check your specific product's label for its exact coverage rate.
The 350 sq ft per gallon figure assumes a reasonably smooth, primed surface. Textured walls, unfinished drywall, brick, or very porous surfaces can soak up noticeably more paint, sometimes cutting real coverage by 20% or more below that standard rate. If your walls fall into any of those categories, treat this calculator's result as a floor rather than a ceiling and consider picking up an extra quart or can just in case.
Paint calculator FAQ
Do I need to subtract windows and doors?
Yes, for an accurate estimate. A standard door is roughly 20 square feet and a standard window is roughly 15 square feet, this calculator subtracts that area automatically based on how many of each you enter.
How much extra should I buy for touch-ups?
It's smart to round up to the next full can or roll rather than buying the exact calculated amount, which this calculator already does. Keeping the leftover on hand also makes future touch-ups much easier since paint batches can vary slightly over time.
Does ceiling paint need a separate calculation?
Yes. Ceilings use a different coverage calculation based on floor area rather than wall height, and often a different paint formulated to resist drips and spatter. Run the ceiling as its own quick calculation using length times width instead of wall perimeter times height.
How much does a gallon of paint typically cover?
This calculator assumes about 350 square feet per gallon for a single coat, which is a commonly cited industry average for interior paint on primed drywall. Always check your specific can's label though, since thicker paints, deep or bold colors, and specialty finishes can cover noticeably less area per gallon.
Why does the calculator round up to a whole gallon instead of showing an exact amount?
Paint is sold in whole gallons and quarts, not arbitrary fractions, so the calculator first rounds your exact coverage need up to the nearest quart, then up again to a full gallon if needed. It's better to have a little extra paint left over for touch-ups than to run short mid-project and have to match a color days later.
Do I need to buy primer separately from what this calculator shows?
Yes, this calculator estimates topcoat paint only, not primer. If you're covering bare drywall, patched areas, stains, or making a drastic color change like painting over a dark wall with a light color, plan on a separate coat of primer using roughly the same 350 sq ft per gallon coverage rate.
Does a textured or porous wall change how much paint I actually need?
Yes, meaningfully. Textured walls, unfinished drywall, brick, and other porous surfaces soak up more paint than the standard 350 sq ft per gallon this calculator assumes, sometimes reducing real coverage by 20% or more. If your walls are textured or unusually porous, treat the calculator's total as a starting point and budget for an extra can.
Doing the painting yourself? The Bates Paint Roller Kit (19 pieces, microfiber sleeves and frame) is a well-reviewed all-in-one pick.
View on AmazonAs an Amazon Associate, QuickAges earns from qualifying purchases.