How to Calculate the Amount of Paint you will Need
For example, you have four walls in your room; you would measure the length and the height of one wall to obtain the square footage of one wall. Next 4 walls x the square footage of one wall equals the total square footage of the room.
Here’s an example using an 8 feet high x10 feet long wall. (8×10= 80 sq. ft.). Next 4 walls x 80 square feet =320 total square feet of the room’s wall surface for painting. Adjust it if needed. For example if you have 5 walls then it would be 5×80 to obtain the square footage of the room walls.
To get the ceiling square footage, just measure your width of the room times the length, and Walla, you have the ceiling square footage total (sq.ft.). 10 foot length x 12 foot width = 120 square feet of ceiling to be painted.
A gallon of paint usually covers 300 sq ft per gallon. In the case 320 square footage, divide on gallon or 300 square feet into 320 square feet. It equals 1. 2. It means it will take over a gallon of paint to cover with one coat. You need to buy one gallon and 1 quart of paint at least. I would recommend you buy 2 gallons, leaving plenty of paint for future touch ups and for the second coat.