Room Dimensions
Subtract Openings
Paint Details
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Gallons Required
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Total Paintable Area (sq ft)
$0.00
Estimated Cost
Estimating how much paint you need is a vital step before heading to the hardware store. Buying too little means an extra trip and struggling to match paint colors from different batches, while buying too much is a waste of money.
The standard formula to calculate paint involves determining the total surface area of your walls. Simply add the lengths of all the walls in the room to get the total perimeter, then multiply that number by the height of the room. For example, a 10x12 room with 8-foot ceilings has a perimeter of 44 feet (10+10+12+12). Multiply 44 by 8 to get 352 gross square feet.
You don't need to paint over your doors and windows, so you can subtract their surface area from your total. The industry standard rule of thumb is to subtract 21 square feet for every standard door and 15 square feet for every standard window.
Using our previous example of 352 gross square feet, if the room has one door (21 sq ft) and two windows (30 sq ft total), your net paintable surface area drops to 301 square feet. Our calculator automatically handles these deductions to provide an accurate estimate.
A single gallon of high-quality interior paint typically covers about 350 to 400 square feet. However, most painting projects require at least two coats for proper coverage, durability, and true color representation. This is especially true if you are painting a light color over a dark color, or if you are painting fresh drywall (which often requires a primer coat first).
Always check the label on your specific paint can for the manufacturer's coverage rate, as it can vary depending on the paint's formulation and finish.