To get basic measurements, measure the length and width of each wall you want to paint in inches. Multiply the length and height together, and divide by 144. This will give you the square footage for each wall. A gallon of paint typically covers around 400 square feet. In some cases, you may need a primer 2 first, then a single coat of paint, meaning that you may need one gallon of primer and one gallon of paint to cover 400 square feet. However, if the wall requires multiple coats, this will increase the total amount of square footage required, and therefore the amount of paint.
Only a dummy gets involved with so-called "contractors." Hire a qualified actual worker yourself. Check out their resume/background, etc. RULE #1..NO ADVANCE DEPOSITS! Pay daily or weekly or upon satisfied completion according your standard, not workers. Contractors are merely employment agents. If that's the way you get work done, then go ahead and waste your money and wind up with the myriad of problems enumerated upon in the news clip above. RULE#2.. NO SMOKERS. They are lighting up on your money. RULE#3: No cell phones while working. Talk on their own time after work