How to Calculate Paint Requirements for a Wall & Ceiling

Measure the length in inches of each wall you want to paint and total these figures on a piece of paper.

Measure the height of the room in inches and multiply this number by the length inch total of the room. Divide this number by 144. This is the total wall square footage you need to paint.

Use the same method to find the ceiling area you need to paint.

Add the two figures you found in step 1 and step 2 to get the total square area of the room. If you are using a different paint finish for the ceiling, which is usually the case, treat these two figures as separate projects.

Measure the length and width of each door and window, and multiply these two figures to find their square area. For windows with circle shapes, measure the window from side to side and divide this number by two to find the radius. Multiply the radius by itself and then by 3.1416 to find the window area. Add together the square area of each door and window in the room.

Subtract the final number you found in step 4 from the total square area of the room in step 3. This is the working area you need to paint. Remember to keep each area to be painted with a different finish as a separate working area.

Go to your favorite hardware store and find the paint you want to use for the room. Read the label on the can of paint to find the square foot you can expect to cover with that can and divide that number by the total square area you calculated for the walls and/or ceiling. That is the number of cans of that size you need to buy for the initial coat. Now, multiply that number by the number of coats you will give to the walls and/or ceiling to arrive at the number of cans you need for the project.