How do you estimate the cost to paint the inside of a house? By square feet? and how much does it cost?

I need to know how to give someone an estimate for painting a house, But I don't know how much to charge them.How do you estimate the cost to paint the inside of a house? By square feet? and how much does it cost?
when you give an estimate consider all these things; how much will the paint cost, not all brands and colors cost the same. what is the degree of difficulty, how much detailing, masking trim,furniture to move ,floors to cover, etc., how many man hours will it take? if you dont figure it out , you will be ,maybe , getting in over your head!How do you estimate the cost to paint the inside of a house? By square feet? and how much does it cost?
I don't estimate by the square foot, I bid by the job. I look at what condition the walls are in (prep adds time and materials), as well as what colors the existing walls are, what they are changing to, whether primer is needed or not, etc. I calculate how many gallons of paint will be required, how many days I will be there, what other materials I will need, and bid accordingly. How fast/good are you? If you splatter paint all over the place, it's hardly fair to charge the customer time for your cleanup. If this is your first time bidding a job, see if you can get the customer to go along with paying you by the hour. Have them get the paint, and settle on a fair hourly rate. Be sure they get good paint, such as Benjamin Moore or Sherwin-Williams. They cost more, but cover better and last longer. Hope this helps.
Wall paint coverage is figured in the following manner:





Dimensions of the room, i.e. 10 feet x 12 feet


standard ceiling height: 8 feet high


10 feet x 8 feet = 80 square feet of wall space for one wall


80 square feet x 2 (number of walls that are 10 feet long) = 160 square feet.


then


12 feet x 8 feet = 96 square feet x 2 = 192 sq feet + 160 = 352 square feet.





you need enough paint to cover 350 to 400 square feet. That's just for one coat. Double it for 2 coats.