We all know that paint is one of the most inexpensive ways to really change the look of a room. Knowing how much paint to buy is important. Buy too much, and you've spent money you didn't need to spend. Buy too little and you have to make a frantic run to the store for more paint. (Not that I've ever had to do that myself, mind you!)
Now, you can always use an online calculator to figure how much paint you need, but I think everyone should know how to do the math, as well. So in case you didn't know, here is a handy guide.
How to calculate wall area
1. Find the perimeter of the room by adding wall lengths. Example: Our example room is 10x12. 10 + 10 + 12 + 12 = 44 ft.
2. Multiply the perimeter by the wall height. A somewhat typical wall height is 8 feet, but measure to be certain. Example: Our example room is pretty standard and has 8 foot ceilings. 44 x 8 = 352 sq. feet
3. Subtract area of doors and windows. If they're an odd size, you can figure the area by multiplying the height x width. Standard doors you can figure on being 20 sq. ft. and standard windows you can figure on being 15 sq. ft. Example: Our example room has 2 doors and 1 window. 20 x 2 = 40 + 15 = 55 sq. ft. Subract from the wall area- 352 - 55 = 297 sq. ft.
So, how much paint do I need?
Most paint manufacturers claim one gallon of paint will cover 400 square feet, but I generally figure on about 300 square feet to one gallon of paint. If you're not changing colors radically from dark to light or from light to dark and are using a good quality paint, you can probably get by with one coat of paint. If you are changing colors radically or are painting your room red (I've always struggled with red!), plan on a *minimum* of two coats, possibly more. So, with our example room we'd need to buy one can of paint if we're not changing the color radically, or at least 2 if we were changing the color quite a bit.
Just remember: if you're in doubt, round up, not down!