How to Measure for a Window Replacement? (Expert Advice)

September 16, 2022

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Performing home repairs and upgrades is a common activity for the majority of the population. Changing the house's old windows is one example of this improvement. Many first-time window replacement homeowners falsely assume that taking measurements is quick and easy. Yet, putting in new panes of glass is more complicated than it may seem. If possible, precise measurements should be used. If not, you can end up with an attractive new window that doesn't work in the space.

It is crucial to take precise measurements of the window opening before replacing an old window with a new one.

Do not forget to measure the frame's outer edges and not just the aperture itself. Companies specializing in window replacement will send someone to your house to take accurate measurements. Measuring windows for replacement is a simple task. But if you mess up on the measurements, things will go south. If you're off by even a centimeter or two while measuring, your new eyewear won't fit. It is essential to ensure that the person installing the new windows takes full responsibility for the measurements.

If you're working with a trustworthy manufacturer and installation, they should handle taking measurements for you. If there is an issue with the window measurements, it will be fixed by the firm.

A professional measuring, on the other hand, costs you nothing. It is a typical aspect of a no-cost consultation. You can obtain a decent understanding of your needs and project costs by measuring the windows yourself, but a free expert measurement will guarantee a flawless fit.

Here are how some expert measures for a window replacement you can use as a ballpark figure when requesting price quotes. Have the installer retake the measurements, though.

house with new windows

Do You Measure Inside or Outside of the Window?

The windows are measured with the greatest accuracy outside of the building.

You should not make the mistake of measuring the window frame. The opening where you will install the window is the one that you should measure. If not, you might as well be measuring a pre-existing frame that doesn't fit well.

If you can see the size of the hole left in the wall after removing an old window, that's the area you need to account for in your calculations. It would help if you reached the opening's brick rim by scraping away insulation and rendering.

Compare the distance between individual bricks.

How is Window Size Measured?

True, you only need to take measurements for height and width. However, you need to take six measures to guarantee accuracy.

The width is measured by the distance between the left and right jambs. It is recommended to take width measurements at the jambs' top, middle, and bottom. Find the person's height by measuring from the top of their head to the center and both sides of the window sill.

Review the window anatomy to ensure that you are taking measurements from the appropriate locations. Your new window will be too small if you unintentionally measure only to the sash stops rather than the jambs or stop verifying the height at the inner sill trim. Your next window will be too huge for the current opening if you go too far past the jambs, head, or sill.

There are various window styles in most residences. Additionally, depending on the style of the window or the presence of trim, you might need to measure a little differently:

  • Measure the height of windows without headers from the drywall at the top to the sill at the bottom; if the window sill has no trim, measure from the wall to the wall.
  • Make sure to take your middle measurements where the two sashes meet in the center of windows with movable sashes.

Write down the smallest height and width after taking six window measurements, not the middle value or the average of the three. When ordering replacement windows, you should err on caution because there is a little more to the window frame than what you can see or measure.

measuring for window replacement

How Much Smaller Should a Replacement Window Be Than the Opening?

Ideally, the windows would be two inches shorter and two inches narrower than the measured area. As a result, there is still an inch of room on either side of the window for positioning and adjusting it to fit precisely where you want it. The windows don't need to be much smaller than the depth; use the measurement to ensure they won't stick out of the frame opening.

Standard Window Sizes Explained

In general, replacement windows are smaller than the ones originally put in your home. This is necessary to ensure a snug fit because the opening in your wall needs to be just a little smaller than the window itself. Additionally, most replacement windows include a trim kit to conceal the window's extra area.

While most window firms provide replacement and retrofit windows, they don't offer window opening modifications or adjustments; instead, they install windows of the same size into the existing opening.

What Are Standard Window Sizes?

When looking for new replacement windows, you'll undoubtedly discover that most of them come in a limited number of standard sizes. The most typical rough opening sizes in homes can accommodate these windows. Although they won't fit every replacement window, it makes sense for manufacturers to create windows that will fit the majority of homes. Try to stick to normal window sizes when purchasing windows to avoid paying more for custom ones.

To assist you in determining the size required for your rough opening, window manufacturers will employ a straightforward size notation for replacement windows. The size of a window is the sum of its width and height. The first two numbers indicate width, while the next two indicate height. A 2426 Replacement Window would be 2'4'' wide and 2'6'' tall. The window's real dimensions are often 1/2 inch less than the whole number identification given.

For instance, a window designated to fit a 44" x 44" opening will measure about 43 12" x 43 12". This is because the manufacturer increases each size dimension by half an inch to make it easier to install the window.

The price of window installation in your home will also depend on your chosen window measurements.

window installation


Home Advisor estimates the average cost to replace a window in a home is $850, ranging from $300 to $2,100 per window. Whether you want a full-frame or retrofit installation, the window material, type, and size you choose, are the most typical elements that can raise the ultimate price.

If you require assistance with home window replacement, please contact our team at Denton Home Window Replacement. Our window installers can take precise measurements for you!

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