by 
The Curious Bag
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<h4 class="dechead">On One Hand: Be Prepared
The amount of paint needed for the inside of a house is determined by the total square foot measurements of the walls and ceilings. Walls that are not completely smooth, have large blemishes, and are darkly painted will require additional paint and primer. Professional painters recommend having on hand at least a quart of extra touch-up paint per room.
On the Other: Less Is More
After measurements have been taken, locate the coverage recommendation on the paint and primer cans that were purchased. The suggested coverage is the amount of square feet that the paint and primer should cover on a normal, smooth surface. Some paint colors are custom tinted at the paint store, which can be costly, based on how much square footage has to be covered.
Bottom Line
Buy more paint than will be needed for touch-up work. If you happen to run short and need to have more paint mixed, you run the risk of getting a different tint than the original paint color.
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