How to Measure Your Windows [2023 Guide] | The Window Experts


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How to Measure Your Windows [2023 Guide]

how to measure your windows [2023 guide]

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Getting accurate window measurements is critical for any project, whether replacing your windows or getting bug screens, curtains, or blinds. You don’t want to order your windows, and when they arrive, they are too big or too small. There’s this saying in the home improvement community: “Get it right the first time.” And it rings especially true for windows, as they perform such an essential role in your home.

In this article, you will learn what you need to correctly measure your windows, how to do it and give you more helpful information on details to consider.

Understanding Window Measurements and Tools Needed

Explanation of Standard Window Dimensions

Canadian laws limit the window’s minimum and maximum sizes and total area. Overall, the window size is calculated by the maximum size of the frame (regardless of its profile), the window type, and the number of panes inside the window panels (not the number of panes inside a frame).

Different Types of Windows and Their Measurements

The governing laws prescribe different minimum and maximum measurements depending on the type of windows. We have assembled a convenient table with all the window information to help you get a good overview.

List of Essential Tools For Accurate Window Measurement

You will not need specialised tools to measure your windows; you will likely already have them in your garage.

You’ll need:

  • A measuring tape
  • A level
  • A pencil
  • A notebook or sheet of paper

Familiarise Yourself with Parts of the Window

Let’s also look at the different parts of the window. Please note that the stool, apron, inside casing and trim, are not considered part of the actual window.

professional window installation

The key terms are:

  • Sash: The part of the window that holds the glass. It can be moveable or fixed.
  • Head: The top part of the frame that touches the top of the sash.
  • Sill: The bottom part of the frame that touches the bottom of the sash.
  • Jambs: The vertical parts on either side of the frame that touch the sides of the sash.

Measuring Window Width

Step-By-Step Guide to Measuring Window Width

Regardless of which material the frame is made out of, the dimensions of all standard windows are presented as width x height.

Begin with measuring the window width from the inside jamb on the left and right side of the window in three places: The bottom, middle and top. Don’t include any of the trim in this measurement.

  • You may have to raise the window sash to expose the jamb at the bottom.
  • Place a tape measure horizontally between the inside jamb on the left and the right.
  • Close the window and make a similar measurement from jamb to jamb near the middle of the window.
  • Measure the distance between the jambs at the top of the window.
  • Record the shortest measurement. This is the window opening width. Make sure to note down all three measurements, as it might be possible that the opening was not well cut and is not parallel.

Please note that even if two windows appear the same size, they may not be. We advise measuring every window individually to avoid potential wrong assumptions.

Common Challenges and How to Overcome Them

One of the most common challenges when measuring your windows is being unprepared. Make a little diagram for every window you have to measure so it’s easy to add the measurements and attribute them to the proper dimension. Also, label them clearly to identify which window they are for.

Measuring Window Height

Step-By-Step Guide to Measuring Window Height

  • Measure the window from the sill to the top of the window opening.
  • It’s important to note that the sill is where the sash rests when it is closed. The horizontal board extending from the wall is the window stool, not the sill.
  • Just like for the width, take three vertical measurements on the left, the centre and the right side.
  • Record the shortest measurement. This is the window opening height. Make sure to note down all three measurements, as it might be possible that the opening was not well cut and is not parallel.

Please note that even if two windows appear the same size, they may not be. We advise measuring every window individually to avoid potential wrong assumptions.

Dealing With Windowsill or Frame Variations

You will need to find the top point of the window sill because if you are dealing with replacement vinyl windows, you are most likely dealing with an old frame. Over the years, frames can warp and twist and will not be straight or level. This is where your level can come in handy, as it’ll help you find the point of the sill (the same goes for the head), and you can measure from those points to ensure that your replacement windows can fit in the frame. 

Ensuring Consistency in Measurement Accuracy

When you measure your window, make sure that for each of the measurements, you choose the same point to get accurate measurements across all points and all windows. Windows are manufactured to these measurements, so ensuring they’re as accurate as possible is crucial.

Measuring Window Depth

Importance of Measuring Window Depth For Proper Installation

When measuring window sizes for replacement, determining the depth of a window might be one of the most challenging tasks. For replacement windows, depth is critical since it will ensure that your window sits flush with the frame rather than sinking in or jutting out, which can lead to problems in the future.

how to measure windows

To ensure you are giving the correct value for depth, you must measure the window opening. Measure between the inside and outside stops to ensure the depth is accurate. If this measurement is less than three and a quarter inch, your measurements are slightly off.

Recording and Documenting Measurements

Importance of Keeping Organised Records

Any wrong measurement can potentially cost hundreds of dollars if the windows don’t fit, so organisation is crucial when measuring windows. It will make it easier to keep track of which windows you have measured and double-check that everything is correct.

Creating a Measurement Chart or Worksheet

Make a small diagram for each window you have to measure and label it accordingly to make it easy to identify later. Write each measurement on the respective part of the window so there are no misunderstandings. Alternatively, you can set up a worksheet with the window location and all dimensions to have everything in one organised sheet and with uniform formatting.

Digital Tools And Apps for Documenting Measurements

If you want to record your measurements digitally, you can use a Google document that can easily be accessed from different devices and quickly shared. You can also check the app store of your mobile device for apps that can help you document measurements.

Window Measurement Considerations for Replacement

The process of measuring windows for replacement or new windows is generally similar, but there are a few key differences to keep in mind:

Existing Window Frame

You must measure the existing window frame from the inside when measuring replacement windows. This ensures that the replacement window will fit within the existing opening.

In contrast, when measuring for new windows, you will be measuring the rough opening in the wall where the new window will be installed. The rough opening is typically larger than the actual size, allowing for proper window installation and insulation.

Frame Removal

When measuring for replacement windows, you need to consider the frame dimensions, including the jamb width and sill height. These measurements help ensure the replacement window fits properly within the existing frame.

In the case of new windows, the frame will be installed along with the window, so you won’t need to measure these dimensions.

Window Style

Whether you are measuring for replacement or new windows, the window style will play a significant role. For replacement windows, you will need to measure the specific style and configuration of the existing window, such as single-hung, double-hung, casement, or sliding. This ensures that the replacement window matches the style and functionality of the original.

When measuring for new windows, you have more flexibility to choose the desired style, size, and configuration.

Condition of the Opening

When measuring replacement windows, it’s essential to assess the condition of the existing opening. Check for any structural issues, rot, or damage that may require repairs before installing the replacement window.

In the case of new windows, the opening is typically prepared and constructed according to the installation requirements of the chosen window style.

In both cases, it’s crucial to measure accurately to ensure the proper fit and functionality of the windows. If you are uncertain or unfamiliar with the process, consulting a professional window company can provide guidance and ensure accurate measurements for your needs.

Measuring Specialty Windows

Measuring Techniques for Specialty Windows

Specialty windows can be tricky to get accurate measurements for. The specific measuring technique can vary depending on the type of specialty window you are dealing with. Here are some general guidelines for measuring different types of specialty windows:

Arched Windows

  • Measure the window’s width at the widest point from side to side.
  • Measure the height from the arch’s highest point to the window’s bottom.
  • Note any additional dimensions required, such as the legs’ height or the arch’s radius.

Bay or Bow Windows

  • Measure the width of the window opening from one side to the other.
  • Measure the height of the window opening from the bottom to the top.
  • Take diagonal measurements from the corners to ensure accuracy.
  • Note any additional dimensions required, such as the angles between sections or the size of individual panels.
bow windows replaced inside shot

Skylight Windows

  • Measure the width and length of the skylight opening from one edge to the other.
  • Measure the depth of the opening from the bottom to the top.
  • Consider any additional dimensions needed, such as the angle or slope of the skylight.

Circular or Round Windows

  • Measure the diameter of the circular window by measuring straight across from one side to the other through the centre.
  • Note any additional dimensions required, such as the depth or thickness of the window.

Geometric or Irregular Shaped Windows

  • Measure the width and height of the window opening at the most comprehensive and tallest points.
  • Take additional measurements for any protrusions, angles, or unique features.
  • Consider using a flexible measuring tape or contour gauge to capture the exact shape of the window.

Remember, accuracy is crucial when measuring specialty windows, as they are often non-standard shapes and sizes. It’s a good practice to double-check your measurements and consult a professional window company to ensure you have the correct dimensions before ordering or installing specialty windows.

Professional Assistance for Accurate Measurements

Especially if you are dealing with windows that are not standard or in difficult-to-reach areas, it might be a good idea to hire professionals. They have the experience and expertise to guarantee accurate measurements even for the most challenging windows.


Accurate window measurements are critical to ensure that your windows will fit perfectly. Wrong measurements can cause significant issues when installing them and cost hundreds, if not thousands, of dollars to fix, so it’s crucial to know how to measure a window.

If you follow the tips on measuring your windows correctly, you can save yourself a lot of headaches. But if you are unsure if your measurements are correct or have specialty windows that make getting accurate measurements challenging, you can call The Window Experts.

The Window Experts have been serving Toronto and the GTA for over 5 years, proudly installing Canadian-made, high-quality windows and doors. We are committed to providing exceptional service to help transform your dream home into a reality, starting with your windows and doors. 

The majority of our business is based on referrals from our satisfied customers. Therefore, we work with integrity to be your number one choice for doors and replacement windows!

Contact us today at 905-875-2596 or fill out our form to schedule a free estimate and learn how we can help you take your windows and doors to the next level!

FAQs About Measuring Windows

You can measure windows from the inside and outside, but the most accurate measurement for a window is outside the building.

Ideally, you should measure the window opening and the entire frame, as with many window types, not the whole window opens.

Different window types have different minimum and maximum sizes and areas of the window. Check our convenient table with all the necessary information to help you get an overview.

You don’t have to remove your windows to measure them. You can take the measurements inside the jambs and between the head and the sill.


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