Things You Will Need
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Measure the height and length of each wall. If the wall has large windows or door frames, measure that area, height x length, and subtract it from that wall's square footage.
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Multiply height x length to calculate square footage.
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Add square footage for each wall together to get the room's total square footage.
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Measure length and width of the floor to calculate square footage of the room's ceiling.
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Choose your paint colors. Deep, dark colors will require a tinted primer and a minimum of 3 coats of paint to get the most uniform coverage. Lighter colors will require only 1-2 coats of paint. Primer may not be required unless you are painting light over dark color.
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Determine how many gallons of paint will be needed. All interior paints specify how many square feet each gallon will cover. Divide the square footage of your room by the paint's square foot coverage amount. This is the amount of gallons needed for one coat. For each additional coat, you will need to double or triple that amount.