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How to Measure Windows for New Ones in 3 Easy Steps?

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It’s time to learn how to measure windows so you can order and install correct sized replacements the first time around.

Once you know how to measure windows, you’ll be able to call in an order in no time.

Q: How to Measure Windows?

A: Good Question! Are you ordering replacement windows or retrofit windows? What’s the smallest measurement from jamb to jamb? Do you need a “three-oh, five-oh” or a “five-oh, three-oh” (3050 or 5030)?

With Do-It-Yourself projects, the first step is “know your medium” – both the parts and the terminology. Then you can get to work. Once you’ve learned how to measure windows properly, you can take a trip to your preferred window vendor and confidently order what you need.

Step 1: Know Your Medium.

Window Vocabulary 101

Suggestion: Print this and take it with you to an open window so you can identify each part as you read about it.

Head – This forms the horizontal portion of the window frame. Not to be confused with the part of the wall, it’s the actual vinyl/plastic/or wood that comprises the outer frame housing the operable or fixed window panel.

Jamb – In wood and vinyl framed windows, the vertical portion of the outer window frame. When you open the window, you can see the jamb. It rests right against the window sash.

Sash – The material surrounding the pane of glass. If you have an operable window, you probably grip the top, side, or bottom of the sash to open the window, depending on the direction your windows operate.

Sill – forms the horizontal bottom of the window frame. It usually has a slight downward slope to keep water from pooling and spilling indoors or damaging your window/wall.

Step 2: Identify exactly what you need to order.

There are two types of replacement windows:

Retrofit replacement window – If your window was broken by an overeager springtime baseball, you would be measuring for a retrofit replacement window. This means your framework is still solid, with little to minimum warping/damage, but something is wrong with the window itself.


New construction replacement window
– This is ordered when you’re either remodeling and changing your entire aesthetic and/or window design, you have done an energy audit and find your window frames are beyond normal lead repair, or perhaps your window frames are badly damaged and need to be replaced.

Step 3: Measure & Record

Note: Window measurements are always given width first, then height.

1. All measurements should be done from the exterior so open the window, head outside with paper and pencil and remove the screen. Draw a simple diagram.

2. Measure the distance between the top of the structural window opening to the bottom.

3. Take three separate measurements from jamb face to jamb face- at the top, middle, and bottom. When you are looking at the jamb face, you will see that there is a small vertical lip in the middle that acts as a guide for the window. You do not want to measure from that lip. You want to measure from the most flat, recessed portion of the jamb face. Record the smallest of these numbers as the width (w). Then take three measurements from the bottom of the head to the top point of the sill slope – at the left, middle, and right. Record the smallest of these numbers as the height (h).

Measuring your windows is that simple! Now you are ready to show off that you know how to measure windows.

Thank you for taking the time to read this article. Call us at 1.877.579.1994 or click here to price your project. Come and see us for a Dan Good Deal at 199 Victoria Street South, Kitchener, ON N2G 2C1.