Windows are essential to any building, providing natural light, ventilation, and aesthetic appeal. However, accurate measurements ensure windows are appropriately sized and installed. Incorrectly measuring a window will result in poorly fitting frames, leading to significant issues and costs such as security issues, draughts, poor energy efficiency, water damage and condensation.
In this article, we’ll discuss the essential steps involved in measuring a window for a new or replacement window as well as the tools required. We’ll also discuss how you can measure your window for a blind installation and why measuring your windows is often best left to a professional window installer.
Tools you’ll need to measure your windows
To start measuring your window, you’ll first want to gather the appropriate tools. To measure for any window, you’ll need the following:
- A metal tape measurer (do not opt for fabric measuring tape as these can be inaccurate)
- A pencil for noting down measurements
- Some paper (loose or notebook)
- A step ladder to measure hard-to-reach places
Preferably you’ll want to measure your window with someone nearby to write down measurements; however, you can write them yourself if you cannot get help.
Measuring the rough window opening
To measure for any window, you’ll need to measure the rough window opening. This opening is the space where your window frame will sit. When visualising a window installation, it can be easy to think that the window frame and the rough opening size will be identical; however, this is incorrect. The window frame size, also known as the net frame size, is typically half an inch to two inches smaller in width and height than the rough opening. This space is to allow for minor adjustments and repositioning.
Finding the rough window opening can vary depending on whether you are replacing or installing a new window. Before measuring, understanding the basic ‘anatomy’ of a window is important to measure the correct parts. In this guide, we’ll talk about the following window parts:
- Sill: the flat surface found at the base of the interior window recess.
- Head: the top horizontal part of the window frame.
- Head jamb: the vertical side on the head of the window.
- Frame: the supportive structure that holds the window and the wall together.
- Side jamb: the vertical parts/sides of the window frame.
- Architrave: the interior moulding or decorative trim that frames your doors or windows inside the home.
How to measure for new windows
If you have already ordered your windows, add a half-inch to two inches to the width and height of the ordered window to find your rough opening measurements. This calculation may vary depending on rough opening recommendations provided by the manufacturer.
If you’re measuring a preexisting rough opening, then you’ll need to follow the below steps:
- Measure the height from the top of the sill to the bottom of the head jamb and record the measurement. If the sill is sloped, measure from the highest point of the sill, typically located right against the window.
- Measure the width of the opening from side jamb to side jamb and record the measurement.
- Measure the opening depth and record the measurement.
Repeat this process for any other window openings. It’s important never to assume that the measurements are identical between windows, as minor variations can impact the size and fit of your window.
How to measure for replacement windows
When measuring for a replacement window, you’ll need to account for the existing installation and how this can affect the accuracy of your measurements.
Below are the steps for measuring replacement windows:
- Using the step ladder, take three vertical measurements of the rough opening height, from left to right, measuring from the head jamb to the sill. Note which measurement is the smallest; this is the rough opening height. If the sill is sloped, measure from the highest point of the sill, typically located right against the window.
- Take three horizontal measurements across the frame from top to bottom from each side jamb using the step ladder. Again, circle the smallest measurement. This is the width of your window’s rough opening.
- Finally, we can measure the depth. Run the tape measure from outside the frame to inside, measuring edge to edge inside the window opening. Repeat this process at three different points of the window frame before taking the smallest measurement. If you can not open the window, measure the depth on each side of the glass.
- Then, add these two measurements together. Finally, add the thickness of your window glass pane. For reference, a single window glass pane is usually 3mm thick. This will give you a rough estimation of the depth of your window opening.
You can now order your windows with your height, width and depth measurements. The windows should, as previously mentioned, be approximately a half-inch to two inches smaller than the rough opening measurements to allow for adjustment and positioning.
In addition to the measurements above, if engaging a professional window installer, be sure to provide as much information as possible, including the window style, room and placement, as well as any problems or challenges you’ve had with the preexisting windows. This information will help your installer provide you with an accurate quote and additional product recommendations.
How to measure windows for blinds
Blinds are an excellent way to enhance the look and functionality of your windows. However, accurate measurements are essential to ensure your blinds fit correctly and look great. Fortunately, measuring for blinds is a lot easier than for replacement windows. Before measuring, however, you’ll need to determine if you want an inside or outside mount.
An inside mount refers to blinds that fit snugly inside the window frame recess. These blinds require a minimum window depth of 60mm to prevent the blinds from protruding past the recess. An outdoor mount refers to blinds that sit outside of the window recess.
Measuring for an inside mount
To measure for an inside mount, measure across the inside of the frame from side jamb to side jamb. Repeat this measurement at both the top and bottom of the window to account for non-square or rectangular windows. Then, measure the length or vertical drop. You can do this by measuring from the top of the inside recess to the base of the window sill. Note down this measurement.
Be sure to always double-check measurements to ensure that you have the most accurate measurement. If you’re measuring multiple windows, clearly label each to avoid confusion.
Measuring for an outside mount
You will need to measure the window architrave for an outside mount. If you don’t have an architrave, add a minimum of 100mm to the width and length of your measurements.
If you have an architrave, measure along the outer edge to find the width. If not, measure along the window opening, adding 100mm to the measurement found.
If you have an architrave, measure the length or vertical drop by starting from the top of the architrave and measuring to where you would like the blind to end. Outside mounts may end at the end of the architrave or all the way to the floor if you’d like.
Again, double-check all measurements to ensure accuracy, clearly labelling window measurements and locations as you progress.
Hiring a window installer
Understanding how to measure your windows for new and replacement installations as well as blind installation, is a great jumping-off point; however, it’s always in your best interest to get a professional installer to confirm your measurements and complete the installation. A professional window installation has many benefits, including:
Professional results
A reputable installer can ensure that your window measurements are accurate and your installation is weatherproof and secure.
Warranty protection
Getting a professional installation ensures that your window is comprehensively warrantied and installed at a high standard.
Specialist tools
Not only will an installer have all the essential measuring tools, but they’ll also have all the tools necessary to install a window, saving you on additional project expenses.
Speedy installation
With an experienced installer on the job, the task will be completed much faster than in a DIY project, especially if this is your first window installation.
Zero-cleanup
A good window installer will ensure they leave your space clean and presentable, saving you the time it takes to clean up after installation.
Product knowledge
A professional window installer will not only know the best way to install your chosen window but can also provide in-depth product knowledge and alternative suggestions to best achieve your desired results.
Measuring a window accurately is important for various reasons, such as ensuring that the window is appropriately sized, correctly installed, and well-suited for your home or building. While measuring windows can be done by yourself, it’s best to leave it to a professional window installer to get accurate recommendations and an estimate. If you’re interested in getting help from a professional installer, contact us today.
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