How to Measure a Window For Replacement

How to Measure Replacement Windows: Tips and Instructions from Experts

You have been saving up for a replacement window. And sure enough, it’s going to update your home’s design, improve energy efficiency, and even translate to better value for your home.

Replacing windows typically means that you will be fitting the new window inside an existing opening. So, it has to fit just right; not too small that it requires extra shimming, and not too large, which could translate to a more expensive fix if you have to reframe the rough opening.

This brings us to the question: How do you get accurate measurements? We’ll cover a step-by-step process on how to measure a window.

That said: Unless you’re installing the replacement window by yourself, don’t stress about getting the dimensions right to a tee. Mad City Windows can dispatch our talented installers to get measurements right.

The Importance of Accurate Window Measurements

Let’s say you’re replacing a 60-year-old wooden double-hung window with a failed window sash. Here’s what can happen if your measurements are too small or if you have failed to properly account for the thickness of the molding covering the vertical length of the window frame:

Improper fit: A smaller frame will not fit properly into the existing opening.
Air and water infiltration: With a larger gap around the frame and casing, air and water may easily infiltrate.
Reduced energy efficiency: As outside air leaks in and inside-conditioned air leaks out, the HVAC system will work harder.
On the other hand, if the replacement window measurements are larger than the opening, it may lead to other issues such as:
Difficult operation: A tight squeeze can make the window very difficult to open and close.
Damage to the existing window frame: Forcing an incorrectly sized window into a smaller opening may potentially warp or damage the window frame.
Uneven appearance: Window frames may appear crooked or uneven if forced into tight uneven openings.

Types of Windows for the Replacement

During the window replacement process, it’s important to consider the different types of replacement windows you may encounter. They include single-hung, double-hung, casement windows, awning, sliding windows, and picture windows.

The general measurement process remains similar across various window styles and only differs slightly with bay (angled) and bow (curved) windows. For these types, the width of each window pane needs to be measured separately, among other considerations.

Step-by-Step Measuring Guide

To measure for replacement windows, there are a few prerequisites to follow to ensure a more accurate measurement:

Check for settling: Remember that houses settle over time, and nothing is perfectly straight. Use a 24″ square to ensure that the frame is within ¼ inch of being square or use the measuring tape diagonally to see if two diagonals are equal. If it’s not square, you may need to consider squaring it up or opting for a full-frame replacement.
Consider exposing the actual frame: For accurate dimensions, it’s wise to remove the casings, moldings, and returns to measure from vinyl to vinyl. You can then add 1/2″ on each side for shims and spray foam.
Compensate for obstructions: If you’re measuring windows from the inside and the end of the frame is obstructed by the molding, interior trim, or spacers, be prepared to compensate for the part you can’t see.
Lastly, gather a few necessary tools: a good brand tape measure, notepad, pencil, step ladder, spirit level, and square (if available).
Step 1: Measure the Width
When referencing new windows, the width is always mentioned first. To measure the width, follow these steps:
Take the width measure from the inside of the jamb (the entire window opening) on each side for accuracy.
Measure horizontally at three places: bottom, middle, and top.
Use the smallest of the three measurements to ensure a snug fit.
Tip: Some manufacturers may include a sticker that provides the window size. If present, it can serve as a helpful reference for the replacement window measure.
Step 2: Measure the Height
To take the height measure of your existing window:
Start at the lowest point of the frame which means measuring from the top of the head jamb to the window sill (account for the stool depth if necessary).
Take the height measure at three points: left, center, and right.
Use the smallest of the three height measurements to avoid fitting issues.
Step 3: Measure Window Depth (If Applicable)
The window depth is simply the length of space between the window pane and the edge of the window casing.
Knowing the depth may come in handy during a pocket window replacement where you don’t wish to interfere with any of the trim or molding.
To measure the depth:
Open the window to access the full depth of the frame.
Measure from front to back where it meets the wall.
Record the smallest measurement.

Common Measurement Mistakes

Getting your measurements wrong by even a small margin could mess up your replacement window. Fortunately, our installers have been doing this for so long that we can tell you the top mistakes to avoid:
Assuming that windows in the same room or next to each other have the same dimensions: Note that each window in a home may be a custom fit and not a standard size.
Failing to account for the real size of the rough openings: While the replacement window is designed to go on top of the existing casing, it’s important to account for the rough openings. This is essential if you opt for more new construction windows with nail fin flange.
Measuring windows from the inside only. Note that it is preferable or even better to get measurements from the exterior if the window is not impeded by the exterior trim.
Not measuring the width and height of the window opening in at least three places. For instance, failing to include all the window height measurements leaves you prone to settling issues or out-of-plumb windows,

Double-Check Your Measurements

It’s going to take some extra time and effort, but you should “measure thrice and install once.” Take your initial set of measurements. Then, take a break and come back for another round of measurements and compare your second set of readings.
If possible, have someone else take their own set of measurements and compare results to replace windows with no issues.
Professional vs. DIY Window Measurement
Measuring an existing window for replacement seems like something you can DIY. But hold on your horses. There is a pretty convincing case, for why you should get the help of professional window installers:
Expertise often translates to better accuracy: A professional installer will be on their hundredth installation of the year, and know all the nuances of frame spacing, sill angles, squaring & plumbing, shimming, and dealing with obstructed frames. On the other hand, if you’re undertaking a DIY replacement, you may not have made your fair share of mistakes to know how to avoid them.
A case of time and effort: With the consideration of having to get both inside and outside measurements, taking all them can become a time-consuming chore. You may be surprised by the endless hours you have to spend second-guessing each detail.
Liability and warranty: The installer will assume liability for installation-related problems arising from measuring window errors and will rectify the issue at no additional cost.

Ordering Replacement Windows

After getting accurate measurements, the next step is placing the order or getting a quote. Here are a few pointers to keep in mind during this process:
Communicate measurements clearly: Provide a detailed diagram or sketch of your windows, including the window width, height, and depth (if needed). Note how the window sash turns or tilts.
Consider custom vinyl windows: Many big box stores will provide standard window sizes. However, due to the variations in architectural features of most homes and owner preferences, you can consider ordering a custom fit. They have slightly longer lead times and a small markup, but the variance should not be too great.
Confirm your order details: Before finalizing your order, take the time to carefully review all the details, including the frame material, glass options, crank & locking mechanisms, and any additional features or accessories.
Plan for delivery and installation: Once you measure windows for DIY installs, prepare all the necessary tools, and materials, and hone your skills. You can confirm the estimated lead time and coordinate the delivery and installation dates.

Conclusion

With the success of your replacement project hinging on getting the right measurements, this is something you should take seriously and approach methodically. Consider the most important things: taking the measurements from vinyl to vinyl, recording the width first, double-checking measurements, and noting how the sash opens.

While DIY measurements may seem appealing in times of cost and wait times, you can benefit from the expertise and reassurance provided by pro replacement window installers. Mad City Windows can offer unmatched support as we facilitate all the steps to the final installation of your new windows. We back up our work with warranties and professionalism you can trust!