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.
this was the estimate i received and well - hard to describe area - double hight ceiling entry foyer plus stairway up to hallway. painted hallway as well with 2 coats plus did a coat of white over all trim/molding/door frames - 6 of them - and repaired some minor molding cracks. we are supplying the paint. at first i thought this was high but then, well, it was better than doing it myself and the painter was highly recommended and he's very nice.
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.

