Anyone tackling their first interior home painting project has likely stood in the paint aisle wondering how many cans they need to bring home. Although the exact amount of necessary paint will depend on factors like brand, wall surface, and how thickly you apply it, you can get a reasonably good estimate of gallons per coat from the square footage you need to cover. To keep your colors matching and avoid return trips to the store, we’ll show you which calculations to do ahead of time.
How Much Paint Is Needed for Walls?
According to Lowe’s, a gallon of primer covers about 200–300 square feet, and a gallon of paint usually covers 350–400 square feet.
- Start by adding up the length of all the walls to be painted, from end to end.
- Then multiply that number (the perimeter) by the height of the walls, from floor to ceiling. That will give you the square footage of the walls.
- If you’d like, you can stop there, which will build a little extra into your estimate. However, if you’d like a more precise estimate, subtract 10 square feet for every window and 20 square feet for every door.
- Multiply this number by the number of coats you plan to paint.
- Finally, divide your total number by the approximate coverage of one gallon of paint (about 400 square feet per gallon) and round up to the nearest whole number. This gives you how many gallons of paint you need to buy.
For example, if a rectangular room has two walls that are 20 feet long and two walls that are 10 feet long, the perimeter of that room would be 20+20+10+10, or 60 feet. If the ceilings are 8 feet high, multiply 60×8 to get 480 square feet. Assuming that there are two windows (2×10=20) and two doors (2×20=40) in the room, subtract 20+40=60 from 480 to get 420 square feet.
If you wanted two coats of paint, you’d multiply 420×2=840 and divide by 400 to get 2.1 gallons. Of course, you can’t buy one-tenth of a gallon, so you’ll need to buy 2 gallons plus a quart or round up to 3 gallons of paint for the walls of that room. A quart of paint can cover about 100 square feet.
More Tips on Wall Paint Coverage:
- Painting white paint over clean, new white paint? Or painting the same color on top of the same color? You might be able to get by with just one coat.
- Porous surfaces like stucco or unpainted drywall absorb paint at a higher rate, so you’ll likely need more paint than the amount calculated.
- Be prepared for future touch-ups with 1–2 extra quarts of paint. Get any custom paint at the same time to ensure evenly matched shades.
How Much Paint Is Needed for Ceilings?
As with the walls, to arrive at the ceiling’s square footage, multiply its length by its width. Then, to determine the gallons of paint needed, divide that number by 400. For the same room as the example above, multiply 20×10 to get 200 square feet. You’ll need half a gallon (2 quarts) of paint for one coat or a full gallon for two coats.
How Much Paint Is Needed for Trim?
A room’s baseboards, windows, doors, and crown molding are often painted in a different finish or color than the walls and ceiling, so you can calculate your trim paint needs separately.
- Add up the length of all the trim to be painted, then add up the width of all the trim. You may need to do this by trim type if they’re not all the same widths.
- Multiply length x width to get the square footage of trim to be painted.
- Divide the total by 400 to get the number of gallons of paint you’ll need for one coat. You’ll likely need less than a gallon for a standard room, so consider buying trim paint in a quart or two.
Let’s go back to that room with a 60-foot perimeter. Let’s say there is 6-inch-wide (0.5 foot) trim that runs the full length of the ceiling. Let’s also imagine that there are 8-inch-wide (0.75 foot) baseboards that cover 52 feet, once you subtract out the width of the doors. The square footage of the ceiling trim is 0.5×60=30 square feet and the square footage of the baseboards is 0.75×52=39 square feet. That’s only a total of 69 square feet, so you’d need 1 quart for one coat of paint or 2 quarts for two.
How Much Primer Do I Need?
Applying primer first helps the paint adhere properly to porous or unpainted surfaces like new drywall, allows for even paint application, and covers up stains. If you’re making a dramatic color switch, a tinted primer in a shade similar to your paint makes coverage easier.
Primer only covers 200–300 square feet per gallon, so you’ll need slightly more primer than paint. Take your earlier total area and divide that number by 300 to get the minimum gallons of primer you’ll need for one coat. From the example above, you’d divide 420 square feet of wall area by 300 to get 1.4, so you’ll need 2 gallons of primer.
How Long Does Paint Last?
Leftover latex paint in a tightly-closed can can last anywhere from a few months to 10 years before going bad. Store all water-based paints in airtight containers to increase their longevity. Unopened cans can last 10 years or more. You’ll know the paint has gone bad if the lid or can itself is bulging, if there’s a film on top of the paint, or if the paint doesn’t mix well or stay mixed. Test old paint on cardboard first to see if it rolls or brushes out smoothly.
Our Conclusion
Buying too much paint wastes money and materials, and while you can always return to the store for more paint if you underestimate, there’s a chance the colors may not match up exactly. Take the time to do the calculations before you head out to the store, and you’ll benefit from less leftover paint—or skip the need to make another trip.
