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Average Window Sizes For Replacement Windows

Written by Carol J Alexander

Published on September 14, 2023


Average Window Sizes For Replacement Windows

When shopping for replacement windows, it helps to know what sizes are standard and when you may need to order one custom-made. This article will have you talking window-speak like a pro.

To provide you with the most accurate and up-to-date information, we consult a number of sources when producing each article, including licensed contractors and industry experts.

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If you plan to install new windows in your home, knowing standard sizes helps you compare options that fit the existing openings. Whether a new home or old, standard sizes vary depending on the type of window. Continue reading to learn about different kinds of home windows, their standard sizes, and when you need custom-made windows.

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What are standard window sizes?

We’re all familiar with standard clothing sizes: S, M, L, and XL. But did you know that windows come in standard sizes? Most homes conform to this standard sizing system, making construction and manufacturing easier. To understand it, you need to learn a few rules.

Width comes before height. So, when writing window dimensions, list the width before the height. 

Window manufacturers assign four-digit codes to windows that indicate size. The first two digits indicate the feet and inches of the width, and the last two indicate the feet and inches of height. For instance, window 2044 is 2 feet, 0 inches wide, and 4 feet, 4 inches tall. Understanding window size notation will help you shop and compare options.

Check out our step-by-step guide on how to measure your windows yourself.

Standard sizes of double-hung or single-hung windows

Single and double-hung windows are the most common windows in homes and similar in appearance. The difference is that only the lower sash moves up and down in a single-hung. But in a double-hung window, both sashes move. This style is preferred for two-story homes where you want to protect children from falling out of the opening. The following sizes are typical for these windows.

  • 2 feet wide by 3 feet high (2030)
  • 2 feet wide by 4 feet 4 inches high (2044)
  • 2 feet 8 inches wide by 4 feet high (2840)
  • 2 feet 8 inches wide by 5 feet 2 inches high (2852)

Standard sliding window sizes

A sliding window has sashes that move from side to side instead of up and down. They provide more airflow and natural light than single- and double-hung windows. And, without the horizontal rail in the middle of the window, the view from a sliding window is unobstructed. Here are the standard sizes of sliding windows. 

  • 3 feet wide by 2 feet high (3020)
  • 3 feet wide by 3 feet high (3030)
  • 5 feet wide by 3 feet high (5030)
  • 6 feet wide by 4 feet high (6040)

Standard sizes of picture windows

For that picture-perfect view, homeowners prefer a picture window. Though they don’t open, the exchange for light and scenery is worth it. They’re often found in the living room or family room. Here are standard picture window sizes to consider.

  • 3 feet wide by 2 feet high (3020)
  • 5 feet wide by 3 feet high (5030)
  • 6 feet wide by 4 feet high (6040)
  • 4 feet wide by 5 feet high (4050)

Standard sizes of awning windows

An awning window is hinged at the top and cranked open. Typically wider than tall, awning windows are commonly used high up in the wall of a mid-century modern design or as a transom above a door. The standard sizes of awning windows include:

  • 3 feet wide by 2 feet high (3020)
  • 4 feet wide by 2 feet 4 inches high (4024)
  • 5 feet wide by 3 feet high (5030)

Standard casement window sizes

Like a sliding window, casement windows lack the horizontal rail that blocks your view of the beautiful outdoors. Usually, they’re taller than they are wide and crank out from the side like a door. Here are the standard sizes for casement windows.

  • 2 feet 4 inches wide by 3 feet 6 inches high (2436)
  • 2 feet 6 inches wide by 4 feet high (2640)
  • 2 feet 8 inches wide by 5 feet high (2850)
  • 3 feet wide by 6 feet high (3060)

Bow window and bay window sizes

Bay and bow windows are created by placing numerous windows side by side. For instance, a bay window generally includes a picture window in the center with a double-hung window on each side. The total size of the bay window depends on the double-hung window sizes and the picture window measurements. Due to these variables, we don’t include standard height or width ranges for these styles. 

How do I measure my window?

To correctly measure your window before ordering a replacement, follow these steps:

  • Make sure your window frame is square by measuring diagonally from corner to corner in both directions. The measurements should be within 1/16- to ⅛- inch the same. If they’re not, you need to hire a professional window installer for this project.
  • Measure the width between the jambs at the widest part three times–at the top, middle, and bottom. The smallest measurement is the width.
  • Measure the height inside the window from top to bottom in three locations–far left, middle, and far right. The smallest measurement is the height.
  • With the window open, measure the depth from the inside of the interior to the inside of the exterior trim. You’ll only need this measurement if you live in a mobile or modular home. Otherwise, all windows are the same depth.
  • Round all the measurements down to the nearest ⅛ -inch.

What is a rough opening?

The rough opening size refers to the frame dimensions that the window attaches to. The frame includes a header at the top, a sill plate across the bottom, and a vertical trimmer on each side. This size is larger than the window size. Once installed, insulation fills the space between the rough opening and the window unit to improve energy efficiency.

What if my window isn’t a standard size?

Older homes may not have common window sizes. If your window opening isn’t a typical size or is an odd shape, you’ll need to order a custom-made window. A custom window will add to the project’s time frame because the window will need to be designed and manufactured. This process includes cutting glass to the desired shape and dimensions and building a frame to match. A custom window is more expensive than purchasing a standard window off the shelf. However, custom window sizes are not limited to standards.

Can you change the size of the window opening?

Absolutely. However, enlarging the size of the window opening is more complex than making it smaller. If you want to widen the space, you must install new studs and new window framing. But if you want to stretch the window’s height, you can leave the sill intact and install a new header. Unless you have construction framing experience, it’s best to hire a professional to expand the size of your window.

To shrink a window opening, you simply need to add wood framing to the existing rough opening. However, homeowners must remember that they have to cover the space on the exterior with new siding or brick. For that, you may need professional help.

Final thoughts

Becoming familiar with different types of windows, common widths, and height ranges helps you make the right decisions for your home improvement projects. If you’re like most homeowners, you’re not ready to DIY a window replacement. Therefore, let us help you find a local window installation specialist.

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Written by

Carol J Alexander Content Specialist and Subject Matter Expert

Carol J Alexander is a home remodeling industry expert for Fixr.com. For more than 15 years as a journalist and content marketer, her in-depth research, interviewing skills, and technical insight have ensured she provides the most accurate and current information on a given topic. Before joining the Fixr team, her personal clients included leaders in the building materials market like Behr Paint Company, CertainTeed, and Chicago Faucet, and national publications like This Old House and Real Homes.