Measure and add up the total width of the walls then multiply it by wall height. Next, divide by the number of square-feet the gallon of paint will cover which is typically 350. A good paint job starts with good prep work. Wipe the walls with the damp cloth then let them dry. Then, apply painter's tape in short sections to the ceiling, baseboards and trim. Seal the edges with the 5-in-1 tool or putty knife. Load a small amount of paint unto a 2-inch brush to outline the walls and ceiling. Start painting by cutting in corners and trim leaving a loosely brushed edge. Load the roller then row paint into the wall in an overlapping W. Fill in the W without lifting the roller to ensure even coverage. Paint the room one wall at a time working from top to bottom. Continue working in 3 foot to 4 foot sections until you are finish with your wall or room. Let the walls dry before removing the tape. Now, you know how to paint a room like a pro. .
As found on Youtube
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