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Rough Opening Size for Windows? (All You Need to Know)

So you are trying to fit a new window into your dream house, but you’re struggling to determine the rough opening for it?

Worry not, as we’ve brought to you all the information you will need regarding this issue, from how to determine the size to the factors that influence a particular size for a window’s rough opening.

Rough Opening Size For Windows

The most common opening size for a window is 3/4th of an inch to an inch more than the frame itself. Although it is not always the case, as the frame and other factors play a role in the dimensions, this is the most common range for this criterion of the windows.

Opening spaces for windows are the empty spaces in the walls where the windows are supposed to be installed. This opening needs to be spacious enough for builders to be able to place and fit the windows without compromising anything.

Different opening sizes of windows impact the amount of daylight admitted into a space, the amount of ventilation, and the amount of energy required to maintain thermal comfort. The rough opening determines how well-fitted the window itself would be.

You have to make sure the opening is large enough to not only fit the window snugly but also allow enough light to pass through the windows.

Generally, the range lies between 3/4th of an inch to 1 inch, sometimes up to 2 inches more than the window frame itself. Here are the rough opening sizes for different kinds and designs of window frames.

Vinyl Windows:

The size of a vinyl window is typically around 2 to 8 feet in both height and width. Based on this, the rough opening size would be about 3/4th of an inch to 1 inch more than the height and width of the window.

Sometimes it can be 2 inches as well, depending on the window size itself.

So, if the window is 2 feet in height, then the rough opening would be 2 feet and 3/4th of an inch or basically 28.25 inches in height, and the same rule applies to the width. 

Andersen Windows:

The average Anderson window is multiple panes, but the number of panes can vary depending on the specific product.

The standard window opening size for Anderson windows is 3’0” wide by 5’0” tall, but they can be as large as 6’0” by 6’8”.

And the rough opening size for these windows is about 3/8th of an inch more than the window frame size.

This means, the rough window opening would measure 36.12 inches wide and 60.12 inches in height for the 3 x 5 feet windows.

Pella Windows:

All Pella windows with wood frames have a standard window opening size. The opening for this type of window is typically 3/4th inch larger than the window itself in both width and height.

You can change the size of the opening to make the window larger or smaller. You can do this by adjusting the installation flange. The installation flange is the part of the window that sits on top of the rough opening.

What Is The Rough Opening For A 36-inch Window?

36-inch windows are the standard size for most houses. Since most people have this size of windows, it is a common concern to know about their opening measurements.

The rough opening size of a window that is 36 inches in size should be about 2 inches more than that of the original size.

What this means is that the 36-inch windows would have an opening of 38 inches wide. Typically that is the gap you get for this type of window, however, sometimes this number may vary ever so slightly.

A rough range that would fit is about 37 to 38 inches for windows that are 36 inches in size. For more precision, it is wise to measure the exact opening size of the windows. If the numbers match, well, you have your answer.  

3 Factors That Affect The Rough Opening Size For Windows

There are mainly 3 points that play a role in determining the rough window opening size for your window. Frame thickness, different window types, and the wide range of manufacturers with all kinds of sizing affect how much space there should be.

Frame Thickness:

One key detail you need to remember is that the thicker your window frame is, the larger rough window opening you are going to need to have.

The main reason for this is that the frame can occupy more space than it should, resulting in less space for fitting the windows.

Measure your window frames properly and check how much space they would actually need. Based on that you have to mark the rough openings. Different windows have different frame thicknesses, so check what yours measures first.

Different Manufacturers:

It comes as no surprise that different manufacturers build windows differently. Although it may seem that a commodity like windows would be made to be universal, the fact remains quite the opposite.

Contrary to popular belief, windows are highly personalized by manufacturers and, well, this affects the rough opening size as well.

Some manufacturers make windows that would need a 3/4th of an inch extra for the opening, while others need a whole 2-inch additional space on each side.

Window Types:

Your window type also determines the rough opening measurements. Different windows such as vinyl, Pella, Anderson, single-hung, arched, bay, and others, have different sizes for the same purpose.

As we said, they just don’t make windows to be universal at all!

Depending on the window model you have and its materials, the rough opening will be determined. The rough opening size for a single-hung window will most certainly not be the same as an arched one.

How Much Space Should Be Between The Window Frame And The Rough Opening?

This is a common question asked by most people wishing to install windows on their own. To be fair, there is no one size fits all answer to this question, however, there is a rough range for most windows that you can use as a reference for your windows.

Your windows would roughly be from 24 inches to 36 inches in size. Let’s say you have a 36-inch window. The rough window opening for this window would be exactly 3/4th of an inch to 2 inches more than the window size itself.

This means the rough opening can either be 36.5 or 36.75, 37, or even 38 inches in size (both in length and width). Typically, the size does not go beyond 2 inches more, however, some exceptional cases may be there.

How Do You Calculate The Rough Opening Of A Window?

Measuring the rough opening size for a window is fairly easy, and does not require any heavy tools or equipment at all. Just grab your trusted measuring tape and get on with it!

Measure the Height Of The Window:

First things first, take measurements of the height of your window. Take your measuring tape and hold it from the top of the frame to the bottom of the frame. After you have taken the readings, write them down on a piece of paper for later calculations.

Measure the Width Of The Window:

Next, very similar to the first step, take the measuring tape and hold it from left to right. From the top of the measuring tape, take the readings at the right-most side of the window. Write down the readings on the piece of paper beside the height of the window.

Measure the Thickness Of The Frame:

Now you are going to have to measure the thickness of the frame. This should typically be anywhere between half an inch to about a couple of inches. Use the measuring tape for this task as well and find the readings. Write them down.

Add the Thickness Measurement to the Height And Width:

At this point, you have all the necessary information to determine the rough opening size for your windows.

Add the height measurement and the thickness, and then you will have the height measurement for the rough opening. Do the same for the width, and you will have its width measurement. 

Final Thoughts

Whether you have large windows or small, the range of the rough window opening size would be about a quarter of an inch to up to 2 inches more than the window’s size itself. As stated above, there are certain factors that play a role in determining this size, so pay attention to those.