How To Measure a Window

How To Measure a Window


Measuring a window accurately is an easy task if you know the right steps. Measuring a window isn’t about taking only the width and height of the window, there are some more things to know when it comes to how to measure a window accurately. Today the experts of have gathered all the necessary useful information about measuring window sizes. This guide will also cover the topic of how to measure for replacement windows. So let’s start with some necessary information about the window parts first.

Important Window Parts To Measure

Window Parts

When measuring a window, it’s important to know the different parts of the window. Below are the window measurement terms that we’ll use in this article.

  • Sash

The window part that holds the glass in place.

  • Head

The top of the window frame that meets the sash.

  • Sill

The bottom of the window frame that supports the sash.

  • Jambs

The sides of the window frame that connect to the sash.

The window has some dressing parts that are important for measurement accuracy. Although they are not parts of the actual window.

  • Sill 

The exterior structural support that protects the window from rain and damage.  

  • Stool 

The interior sill, a flat shelf-like portion inside the window.

  • Apron 

A decorative cover that hides the space between the wall and window frame.

  • Weep holes

Small holes that allow water to drain out and prevent moisture buildup.

  • Inside casing/trim

Decorative coverings that cover the spaces between the window frame and wall.

Steps To Measure Windows

How To Measure a Window

Now you know about the widow parts, you can easily measure a window. Remember to always measure twice to ensure accuracy. Measure the window opening from the outside, not the frame. Measure the hole where the window sits, from brick to brick, ignoring the frame. This ensures an accurate measurement, even if the old frame was installed poorly.

Measure Window Width

Measure Window Width

Use a measuring tape to measure the window opening width at the top, middle, and bottom, from the jamb surface to the jamb surface. Order the window using the smallest window height.

Measure Window Height

Measure Window Height

Use your measuring tape to measure the window opening height from the sill to the top of the opening at three points (left, center, right). Order the window using the smallest window height.

Measure Window Depth

Measure Window Depth

Ignore the sliding parts and small strips and measure the frame depth from the interior stop to the exterior stop. Ensure a minimum depth of 3-1/4 inches to accommodate the replacement window.

Check If The Window is Square

Check If The Window is Square

Measure diagonally from the top right where the horizontal and vertical window jambs meet to the bottom left where the trim meets. Now measure diagonally from top left to bottom right. Record both measurements. If they’re within 1/4 inch of each other, the window will fit.

How To Measure for Window Replacement

How To Measure for Window Replacement

If you are measuring for window replacement, start by measuring window width, height, and depth. Take three measurements for width, one from either side of the and one from the center horizontally. Do this for measuring the height too but vertically. Take the smallest readings. Now measure the frame depth by measuring from the front edge of the window frame to the back edge, either from the interior or exterior.

How To Measure For Storm Windows

How To Measure For Storm Windows

You can measure storm windows like regular windows for example single hung or double hung.

  • Width

Measure inside trim, left to right, at bottom, middle, and top. Use the smallest measurement.

  • Height

Measure from sill to top trim, left, center, and right. Use the smallest measurement.

Remember, using the smallest measurements ensures a proper fit inside the window opening.

How To Measure For Window Screens

How To Measure For Window Screens

If you have window screens to measure, simply measure the window screen size width and height. Measure between horizontal channels, then subtract 1/8 inch to calculate its width. Measure from lip to sash (with the window open), then add 1/8 inch to calculate its height. You can use these measurements to find the right screen size for the window.

How To Measure Bay Windows

How To Measure Bay Windows

Most homes have bay windows to give a beautiful view of the surroundings. If you want to measure bay or bow windows, just follow the below steps.

  • Measure each window pane separately, starting with the middle one.
  • Measure its width horizontally from trim to trim (or jamb to jamb).
  • Measure height vertically from trim to trim.
  • Record the width and height for each pane.

Final Measurement Check

After taking all the calculations and measurements, double-check and finalize them. 

  • Measure each window individually, don’t assume the same dimensions.
  • Use the shortest width and height measurements for each window.
  • Record measurements in width x height format (e.g., 24 3/8″ x 40 1/4″).
  • Round down to the nearest 1/8 inch (e.g., 24 15/16″ becomes 24 7/8″).
  • If already in 1/8 inch increments, no adjustment is needed.
  • Use these measurements to order your replacement windows.

Keep in mind that accurate measurements are crucial for proper installation, so take your time and measure carefully.

Order Your Required Replacement Windows

Now you can order your windows from a company or retailer of your choice. You can visit a local hardware store or a retailer for purchase. However, be aware that their windows might not fit right. To ensure a precise fit, consider ordering custom windows that match your exact dimensions. You can also compare Marvin vs Andersen windows if you want integrity and high-quality glass for your windows. 

Frequently Asked Questions (FAQs)

What Size Replacement Window Should I Order?

You should order replacement windows using your measurements. Measure the width and height of your window to ensure a snug, draft-free fit.

Why is it Important To Measure a Window Accurately?

Accurate measurements ensure a proper fit for replacement windows, window treatments, and energy efficiency.

How Do I Measure The Width Of a Window?

Measure from the left edge to the right edge of the window frame to accurately calculate window width.

How Do I Measure The Height Of a Window?

You can measure window height by calculating the distance from the top edge to the bottom edge of the window frame.

What is Window Depth, and How Do I Measure it?

Window depth is the distance from the front edge to the back edge of the window frame. You can measure it from the interior or exterior, depending on your needs.