How to: Painting A Room and Estimating Paint

How to Painting A Room and Estimating Paint Featured image

Before you begin painting a room it’s important to first estimate how much paint your walls will need. Estimating paint for a room depends on a few factors such as the texture of the wall, your paint application method, the quality of your interior paint, and the paint color you decide upon. First measure the length and height of your walls, multiply these two numbers together to find out the actual square footage of the walls and surfaces in the room you plan on painting:

Room in painting process

Ft length x Ft height = Sq

uare footage to be painted

If there happen to be large areas of the walls that will not be painted, for instance French doors or large bay windows, simply calculate the square footage of those areas and subtract them from the area you plan on painting. This will allow you to take into account the actual amount of paint needed for your room.

As a basic rule of thumbs for walls…

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 room to be painted.

Finally, divide your total number by the approximate coverage of one gallon of paint (about 400 sq. ft. per gal.). This gives you how many gallons of paint you need for one coat of paint on the walls.

The majority of paint manufacturers label on their paints the expected area of coverage. Since most manufacturers are optimistic about their coating products use this as a rule of thumb and consider subtracting up to 10% from what is listed on the can to ensure you have enough paint. For instance, if the paint can claims it can cover 350 sq ft, plan on it covering 320 sq ft this will give you a better margin for error. The last thing you will want is to drive out to the paint store for more product to cover a few measly sq ft!

Always plan on painting two coats

95% of the time when you are painting a room you will need two coats of paint. It’s rare that one coat will provide a solid well finished wall so do not plan on this outcome. Multiply your total square footage by 2 to get a fairly good measure of the paint requirements for two coats. It should be noted that your second coat of paint can use cover a little more area but it’s a good idea to not get overly optimistic about your paint coverage and use the safe assumption that your second coat will take as much paint as your first. Consider multiplying your initial one coat square footage by only 1.95 if you are feeling lucky on your second coat.

At times a primer will be needed

Primers can do a variety of tasks such as covering an old wall paint color and getting it ready for a fresh coat of paint, and even covering up stains so they don’t bleed through your new paint job. If you’re unsure whether to use a primer you can ask one of the workers at your local paint store and describe your situation. Getting this right can save you a lot of hassle when you’re painting your walls later.

Wall texture will affect paint absorption

One aspect of estimating paint for your room is the texture on the walls. If you have smooth walls you will need far less paint compared with heavily textured walls. A wall with a heavy texture will have more surface area overall because of the grooves or bumps, this will cause more paint to be required to effectively cover the entire surface. Further, sometimes paint will literally soak into these small grooves. In order to insure effective and efficient painting you should also consider your application method, opting to spray or use a thick napped roller sleeve if your surface is very heavily textured. I would consider adding up to 35% more paint if you are painting an excessively textured surface.

Paint application method must be considered

When painting a room your application method can affect how much paint is wasted and thus how much paint will be required overall. When using a traditional paint roller and paint brush do not expect much waste associated with your paint job. Most sprayers require at least a quart to be primed before you can actually use the tool, so remember to keep this in mind. Application method can add up to another 20% of paint requirements. If you are very inexperienced you may want to consider adding 5% as margin of error.

Interior paint quality can affect paint coverage

The quality of your paint will affect the coverage and spread rate. When considering standard conditions, higher quality interior paint will be able to cover more square footage than lower quality paint. This is especially true when considering the usage of bold or deep colors such as red, purple, and yellow. See paint color for more on this.

Paint color will require your attention

When estimating paint for a room the color you decide to paint your room will have an effect on the amount of paint you will need. If you are interested in painting your room a bold or deep color be prepared to paint up to three coats of paint. If you are using a top-end paint product you can expect to paint two coats, for instance Benjamin Moore Aura can create a fantastic red color with only two coats of paint. This is unheard of in the majority of paint brands so it is advised you consult your paint supplier to ensure you have the right product for the job at hand.

Armed with some knowledge, let’s now take a look at an imaginary room painting estimate:

Our imaginary room is a 10×20 room with 8 ft. high ceilings, fairly textured walls, and we plan on using two coats of decent quality paint

First figure out how much area needs to be painted:
10 x 8 = 80 x 2 walls = 160
20 x 8 = 160 x 2 walls = 320
4 walls = 480 sq ft

Calculate extra surface area because of the texture:
480 sq ft x 1.2 (20% extra for texture) = 576 sq ft

We’ll use a straight 2 coat estimate, because of the texture we don’t want to take any chances:
576 sq ft x 2 coats = 1152 sq ft total coverage of paint needed

Now let’s figure out how many gallons we need, our paint claims 400-450 sq ft coverage so again let’s err on the side of caution and use the lower estimate:
1152 sq ft total coverage of paint needed / 400 sq ft paint coverage = 2.88 gallons of paint

Let’s plan on buying 3 gallons of paint to get a good coverage on this room.

As you can see there are a few factors to take into consideration when calculating how much paint you will end up needing to paint a room properly. Estimating paint requirements is a bit of an art form, this is a skill that will develop as you gain experience painting. I hope this write up has been of service and provided you with a good idea of how to estimate paint when painting a room.

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