Take the Guess Work Out of Painting

Many people have leftover paint because it’s not easy to know how much paint to purchase in the first place. Most homeowners and DIYers who paint occasionally need help estimating the right amount of paint needed for their projects. They simply lack the experience that a professional painter has in estimating how much paint is needed for the job at hand.

When estimating how much paint you need, there are several variables to take into account. We always recommend measuring your room, bringing your measurements to the paint store, and asking the staff for help figuring out how much paint to buy.

Below are the types of questions your paint store expert may ask in order to give you the best advice. Being ready to answer these questions will help determine how much paint you need for your next project.


1. What is the square footage?

The first thing to determine is the size of the surface you want to paint. You’ll need to know the surface area of the walls of a room or the outside of your house. Most paint companies feature calculator tools on their websites that allow you to enter room dimensions to calculate an estimate of how much paint to buy. The results from these calculators vary because coverage rates vary by brand and quality.

To calculate the size of your space, measure the width and height of each wall. For each wall, multiply the width times the height to get the square footage. Add the square footages together to get the total. Then measure any windows, doors, or other breaks in the wall and subtract their square footage from your original calculation. Now you have the area – the number of square feet you need to cover.

Divide the area by the coverage rate, if you know it. (Check the label on the can.) If you don’t know the coverage rate, use 350 to get a rough estimate. Most coverage rates are between 300-400 square feet per gallon. For example, the square footage of a 10’x10’ room with a ceiling height of 10 feet is about 400 square feet. If the coverage rate is 400 square feet per gallon, you’d need one gallon. If the coverage rate is 300 square feet per gallon, you’d need 1.33 gallons. After subtracting windows and doors, you’d probably only need one gallon for a typical 10’x10’ room.

By the same method, a 20’x20’ room (with 10 feet ceilings), would probably need two gallons.

These figures are just a start. You also need to take the following factors into account.


2. Are you making a big color change?

If the new paint color is similar to the old paint color, you will need fewer coats. However, if you change from a very dark color to a very light color, or from a very light to a very dark one, you may need three, or even four coats.

Some vibrant and dark colors, especially red, orange and purple, may take even more coats to get an even finish.


3. Is the surface textured?

Textured walls require more paint than smooth walls because all those bumps mean that a textured surface actually has more surface area than a smooth one . The greater the texture, the more paint is needed — you may need up to 50 percent more paint for rough textures.


4. What sheen? Shiny or flat?

As sheen decreases, coverage increases. Flat paints require less paint to cover, while semi-gloss and glossy paints require more paint. Generally, a job that takes two coats of flat paint typically takes three or more coats of semi-gloss or glossy paint.


5. Have you used primer?

New, unprimed drywall, plaster, and bare wood absorb more paint and require more coats than surfaces that have already been primed or painted with a base coat. Besides helping to achieve better adhesion, primer fills in tiny surface holes. Primer prevents the top coat from being absorbed and reduces the number of coats needed.

Although primer is usually white, you can often ask your paint retailer to tint primer so that the color of the primer is closer to the final color. This will reduce the number of coats you’ll need.

Primers are usually less expensive than paint, and they are specially formulated to improve adhesion and fill porous surfaces. You can also use up paint leftover from a previous project by applying it as a base coat to even out the surface and color.


6. Do you need tinted primer?

Consider using tinted primer for certain color changes. Some paint retailers will tint primer for you, but you should know that there are limitations to how much pigment can be added to primer. The color will not be the same as the final coat, but tinting primer will reduce the number of top coats you’ll need. Note: use gray primer when changing the wall color to red.

An unopened can of paint can last for decades if it is stored in a dry, cool (but not too cold), dark place. It’s best not to leave any paint cans in sunlight, outdoors, or in a damp location. Most of your cans were probably opened and still have some paint that you might want to use for touch ups or another project. Even if you think you will get rid of your leftovers, follow these tips to keep your paint in better condition so someone else can use it or recycle it.

Opening and Closing

Don’t be Reckless with the Rim

When opening the can, use a paint key instead of a typical screwdriver because it will bend, distort, or otherwise damage the lid, making it difficult to put back on. You can pick up a paint key or paint can opener, wherever you purchase paint.

  • When putting the lid back on the can, tap it with a rubber mallet instead of pounding it with a hammer.
  • If you don’t have a mallet, place a piece of wood or an old book (or even a thick magazine) between the hammer and the lid and then carefully tap it down.

Keep the Rim Clean

If you wipe the edge of your brush on the rim of a paint can, you will end up with a rim full of accumulated paint. If you finsh the can, that’s not a problem, but if you want to reseal the can and save the paint, you will have trouble getting the lid on tight. Follow these tips to keep the rim clean:

  • Poke holes in the rim with a medium size nail or awl so that paint drips back into the can and doesn’t accumulate in the rim.
  • By taping the rim of a paint can into the shape of a “V” or an arrow, it provides a clean pour that leaves the rim clear for an easy clean up.
  • Wipe out the rim regularly while you are working and just before putting on the lid.
  • If the paint has dried in the rim, you can try to pry it out before replacing the lid – but be careful not to drop any dried paint into the can.

While You are Working

  • When you are using a brush, pour paint from the original can into another container (such as a plastic quart container sold at most paint stores), then dip your brush into the container, rather than the original can. This will also allow you to close the original can while you are working and keep air from drying out the paint.
  • By securely strapping a rubber band around the top of the paint can, it can be used to clean the edge of a paint brush – making a more efficient painting experience.

Closing Up

  • Cover the opening with a piece of plastic wrap before putting on the lid. The plastic will act as a gasket creating, a tighter seal.
  • You may have heard that you should put on the lid, then turn the can upside down, but it’s not necessary. If the lid is on tight, there is no reason to turn the can upside down. Rather than take a chance that you didn’t put the lid on tight, just check it one more time.

Storage Location

Keep from Freezing

Water-based paint labels normally say “keep from freezing,” but did you know that paint may still be usable even after it freezes once or twice? If you can stir paint into a smooth consistency, it’s still good. If it freezes and thaws several times, it will get worse each time. If you stir paint and it stays lumpy and never gets smooth, it’s spoiled.

Keep Out of the Rain or Damp Locations

When cans get wet, they will rust and the labels will fall off. Even plastic cans have metal lids that can rust. Rusty cans and lids make a mess and fall apart when you handle them, and the rust will fall into the paint, making it unusable. If the label falls off, you won’t know what type of paint or color is in the can. Keep your paint dry.

Marking Paint Cans

To indicate the level and color of paint in a particular can, use a brush to paint a line on the exterior of the paint can. Use the same color as the paint that is inside the can. Use a permanent marker to write a note on the side that will tell you when you bought the paint and where you got it. Include a brief description of the room or wall that the paint has been used on, as well.

Using up what you have is a great way to reduce leftover paint.
Here are a few ideas to get you started.


More than a gallon

Use light shades as primers for other paint projects, or donate to a friend, neighbor, or local organization who can use it.


Less than a gallon

Consider painting a small room, like a bathroom or a closet, or experiment with accent walls, a wall with many windows, or a wall that flanks stairs. You can also recoat a scuffed up piece of furniture.
Indoors isn’t your style? Paint the brick or stone edging around your garden, or protect an old fence from weathering.


A quart

A quart is perfect for updating a window frame or two, coordinating picture frames, brightening up the inside of a bookshelf, or creating a color pop inside a nightstand.


A pint

Personalize a tray, color a glass vase, dip the handles of your tool set, update a table lamp, or make a playful stool by dipping its legs in what you have left.


Sample sizes

Cheer up a bird house, coordinate door knobs, make a playful candle stick, trim the edge of a mirror, stencil a tote bag, or dip some canvas shoes.

Reuse includes giving paint away

Do you have some paint in good condition that someone else can use? Here are some ideas on how to find someone might be interested in your leftover paint:

Friends and Relatives

Have your friends or relatives commented on how much they admire the colors you selected for your home? Offer them the leftovers.

Community Groups

Churches, Schools and nonprofit organizations that do community housing projects (e.g., Habitat for Humanity) may be able to use leftover paint in good condition.


School and artists groups that create murals or do painting projects may be interested in paint for murals and other art projects. They are often interested in white or light colors that can be tinted to new colors, or smaller containers of samples and bright colors.

Garage Sales

Having a garage sale? Put out your leftover paint with that pasta machine. Someone else may be looking for just what you don’t need anymore. It’s a win-win. They get a good deal, you make a few dollars, the paint gets reused, and it’s better than recycling.

Free Online Listings

Try listing your usable paint on websites such as freecycle.org or craigslist.org either at low cost or for free. You never know when someone will be looking for a good deal on some good paint.

Recycle the Rest

When you’ve run out of ways to use up your leftover paint, recycle it with PaintCare.

  1. Know what types of paint can be accepted: Program Products
  2. Learn how to prepare your paint for drop off: How to Recycle
  3. Find a PaintCare drop-off site near you: PaintCare  Site Locator

Before dropping off paint, please call the site to check business hours and make sure they
can accept the type and amount of paint you would like to recycle.cans-many