How to Measure Windows for Replacement

measure windows

Why Measuring Replacement Windows Is So Critical

There are few things more important in the window replacement process than the measurements. You’ve heard it said, “Measure twice, cut once.” and with replacement windows that axiom is especially poignant. Replacement windows are expensive and lead times are typically weeks, if not months. Having to reorder is not only costly but get causes serious delays in your project. Additionally, a properly sized window is going to perform better, look better, and last longer than a window that is either over or undersized. Contact us for your window replacement and installation needs today!

If the window is too small not only will the end result be ugly due to the excessive caulking or trim that is needed to fill in the gap; but an undersized window is much more difficult to properly seal so the likelihood of a leaky, drafty window is greater. While an oversized window is an even bigger problem. Making the opening bigger isn’t a very good option as it’s difficult and costly, particularly in brick. It’s much more likely that you’d end up just reordering the right size and waiting several more weeks for your new window.

The good news is that it’s not difficult to do, you just need to be patient and precise to be successful. Before you begin, ensure that you have what you need to be safe. A good ladder is a must as the best way to get accurate measurements is from the outside of the house. Even if your home is a single story, you still need to be able to reach the top of the window for a good measurement.

Before We Begin

The process that we’re going to outline below generally applies to replacing any type of window with any type of window with the exception of wood or clad-wood windows, either replacing existing wood windows or going back in with wood windows. There are a few ways to go about it depending on your situation so you’ll really want to consult with an expert on a project involving wood windows.

Things you’ll need to measure your windows

  • Tape measure
  • Adequately sized, stable ladder
  • Notepad or clipboard
  • Pen or pencil
  • Level
  • Plumb bob

Pro Tip

Before you begin, make a sketch of a top-down view of your house. It doesn’t have to be pretty or to scale but it’s really going to help you out. Face your home and number the first-floor openings from left to right starting at the left corner then if you have a two-story home pick up the sequence once again and number around the second floor.

Now, as you start recording measurements for your windows number them accordingly and note the window type. Using SH for single-hung, DH for double-hung, P for picture, CS for casement, HS for horizontal-slider, etc. For example:

  1. 37 1/2″ x 59 1/4″ SH
  2. 37 5/8″ X 59 3/8″ SH
  3. 47 3/4″ x 47 1/2″ P
diagram for measuring windows for replacement

How to Measure For Replacement Windows In Brick

While replacing a window in brick seems like it would be the most daunting since it’s the least forgiving but if measured correctly it’s pretty straightforward. Keep in mind that you’ll order your windows without a nailing fin since you’ll have to do a block-frame installation. Before you begin, check the window to make sure it’s relatively level, plumb, and square. Since windows need to be installed level, plumb, and square to properly operate and drain it follows that the opening should be as well. Let’s say that a brick opening is really out of square by one inch. Meaning, if you hung a string from the top corner there was one inch of space between the bottom corner and the string. In a situation like this, you need to consider measuring the window to fit square, plumb, and level and trimming out the gap. It may not look pretty but at least you have a window that functions. Situations like this are pretty rare but I want you to be aware that it does happen.

Assuming that your opening passes the square, plumb, and level test, you’ll first measure the width (windows are always measured in WIDTH X HEIGHT) of the window in at least three places, bottom, middle, and top. If the window is especially tall, say eight feet or more, then you’ll want to take two measurements in the middle about a third of the way from the top and bottom. Also, if there is some brick that is clearly protruding into the opening you need to include it as one of your measurement points or decide if you’re willing to chip it down to get a better all-around fit. As we mentioned before, measure each point twice (at least).

Once you have your width measurements take the shortest of the batch and make your deduction for fit. Keep in mind that whatever you deduct will give you the gap that you need to get the window into place. There’s no “industry standard” here and it’s really up to you but I recommend nothing less than half an inch. This will give you a quarter of an inch on each side of the window which gives you room to work and can easily be foamed and caulked to provide a good seal. For example, if your shortest window measurement is 35 3/4″ then a 1/2″ deduction would give you a final figure of 35 1/4″

The measuring process is repeated on the height of the window, making all of the same considerations as outlined in the previous paragraph.

How to Measure For Replacement Windows In Siding

The same basic principles apply for measuring windows in siding but since you’re working with trim and siding you have a few more options. First, you can just go with the block frame installation like with brick but since the band around the window can be removed you do have the option of using a nail fin for installation. If you go this route, you’d remove the trim around the window, attach the replacement window directly to the sheathing of the home, flash it with flashing tape, and put up new trim.

Also, since siding is more forgiving than brick if an opening is really out of square it’s a lot easier to fix the opening to accommodate a replacement window instead of just working with what you have as in the case of a bricked opening.

How to Measure For Replacement Windows In Stucco

In measuring for replacement windows in stucco we’re really dealing with a brick meets siding scenario. If your stucco has a protruding band around the windows then you have the option of hiring a stucco contractor to remove it, then installing the replacement windows with the nail fin, and having the stucco contractor rebuild the band. Yes, it’s more costly but it’s going to look like it did when the home was built.

The second option is to order the windows with what is called a stucco fin. This is a perpendicular extension of the frame that will overlap the existing stucco because in the process of removing the windows there will certainly be some damage to the existing stucco. A stucco fin installation is a good way to complete a window replacement project in an effective but price-conscious manner.

stucco fin
Stucco Fin

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