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.
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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.
Coverage figures reflect commonly cited paint-industry averages, always check your specific product's label for its exact coverage rate.
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.