Take for example, I charge 1.75 sq foot for 10x10 room with 8 foot ceilings. By my calculations this would cost $175 with floor space sq foot, but with you method, it would cost $576.00 That is outrageous. Of course I didn't subtract the windows and doors, which is another thing that makes no sense. Cutting in around those windows takes more time, then just rolling a wall.
5383 actual square footage of walls. Do not estimate or accept estimates based on square footage of floor. I use a laser device to ACCURATELY measure. I take out for windows and doors. Unless a job is new construction (empty), understand that furniture,artwork, carpet, appliances, etc. will affect time and labor. Also understand that ceiling height is a game changer. A rate of no less than $1.80/sf including materials is realistic, acceptable and more than fair for a qualified professional to paint rooms with 9' ceilings. Expect to pay $1 extra per square foot for 9'- 15' and $2.50 extra for 15' +. Some additional costs for extreme conditions will raise that amount. Trying to base the amount on days worked by number of workers is both unfair to the professional and undue to your senses. This job is based on 15 days work by two workers, one painter and one grunt to tarp, move furniture, clean up and book paint. That nets to approx $663/day. As you can see, not great wages.
I was a professional painter way way back for a company. Now I am dabbling in working around the neighborhood here and there and needed to know how much I should charge. I recently painted an entire home including woodwork / doors / windows/ baseboards and the paint costs $230 ish and I did it free for my best friend . It took me 4 days to do . 7am-9pm . It turned out absolutely beautiful , and every room was a different color .
"Rafael was very professional, detail-oriented, pleasant to communicate with (responds promptly, returns calls, confirms appointments) and always showed up on time. He painted my daughter's room beautifully and for a reasonable price (offered pricing with and without paint). His work was precise and without mess. I will definitely hire him again for more painting projects."