Expert Advice: Proper Paint Amount

Painting expert Brian Santos reveals the formula for buying enough paint for your project. Read more in his new book, "Painting Secrets."
From Painting Secrets from Brian Santos The Wall Wizard




Author Brian Santos
Q. How much paint should I buy?
Brian Santos: If you're not a numbers person, the following steps may sound like gibberish. Just take it slowly and break out each step -- at the end you'll arrive at an accurate estimate for the amount of paint you need.




Simple Calculation:
1. Calculate the square footage of the surfaces to be painted. Measure the length and width of the room and determine its perimeter, which is the distance all around the room. For example, if the room is 13 feet wide and 18 feet long, its perimeter is 62 feet (13 feet + 13 feet + 18 feet + 18 feet).
2. Multiply the perimeter by the room's height to get the square footage of wall space. If the room is 8 feet high, then its square footage is 496 square feet (62 feet x 8 feet).
3. Count the doors and windows in the room. Subtract from your wall area 21 square feet for each standard door and 15 square feet for each standard window. (If your room has large doors, such as a sliding patio door, or large windows, you can measure the width and height of each door and window, then figure the exact square footage of each. You don't need to be precise; round to the nearest square foot.)
4. To find the number of gallons of paint needed, divide the wall area by 300 -- the square footage easily covered by a gallon of interior paint.

Quick Tips:
After that lesson in estimating, you'll be relieved to learn these tried-and-true Wall Wizard tricks.
A gallon of paint will cover about 300 square feet of wall area. Some manufacturers stretch it to 400 square feet, but go with the lesser amount to keep from running out of paint in the middle of a job.
Always buy more paint than you need. This extra amount allows for spillage, waste, and spots that soak up more paint than expected. Plaster, for example, is more absorbent than wallboard. Also, you'll want leftover paint for future touch-ups. Remember to buy extra paint if you plant to paint the interiors of built-in bookshelves or cabinets.
Another reason to buy more paint? Custom-mixed colors vary slightly from batch to batch, so it's best to buy enough paint at one time instead of running out and having to match the colors.
If you can't decide between 4 or 5 gallons, go with 5 and buy it in a 5-gallon container. It should actually be cheaper than three 1-gallon cans, and you're guaranteed the colors will be the same.