How To Calculate The Amount Of Paint Needed For A Space

updated May 7, 2019
We independently select these products—if you buy from one of our links, we may earn a commission. All prices were accurate at the time of publishing.

One of the easiest ways to live a green lifestyle is to simply buy only what you need. This is especially true when it comes to painting your spaces. Sure, it’s nice to have a small amount for touch-ups down the road, but that doesn’t mean you want rogue half gallons (or even whole!) sitting in your garage taking up space! Eliminate the waste and buy the correct amount to begin with. Here’s how:

What You Need


Measuring Tape


1. Measure The Length Of Your Wall: Have a friend or family member help you hold a tape measure to get an accurate reading. Measure wall to wall and not against the floor where molding might lessen the amount needed.

2. Measure The Height Of Your Wall: Again with assistance, measure the height of your walls from floor to ceiling (note baseboard to molding).

3. Multiply The Two Numbers: This gives you the square footage of your wall. Repeat the process for all the walls needing to be painted and add their square footages together to give you the total amount of space needing to be painted.

4. Dive That Number By 400: When it comes to buying paint in gallons, 400 is the magic number. That’s how many square feet each can will cover. So by dividing your square footage by 400 will tell you how many cans you in fact need!


20 ft (wall length) x 8.5 ft (wall height) x 4 (number of walls that are the same size) ÷ 400 (how much sqft each gallon covers = 1.7 gallons needed (for one coat)

Additional Notes: Remember to increase this number accordingly for the amount of coats needed (for paint and primer both). Don’t be afraid to purchase a whole gallon and smaller pint sizes to come out with the right amount of paint so you don’t have that half empty can hanging out for years!

Image: flickr member ewen and donabel licensed for use by Creative Commons