Standard window size guide: Common dimensions for every window type

• Standard window sizes vary based on the type of window, such as single-hung, casement, or sliding.
• Older or historic homes often have non-standard window sizes that require custom replacements.
• Custom or oversized windows are more expensive due to increased material costs and complex installation.

Whether you’re purchasing new windows for your home, renovating, or buying a new construction, understanding standard window sizes will help you make the most informed decision. Many homes use common window dimensions, but not all windows fall into these “standard” sizes. 

The type of window, its size and the age of your home all play a role when calculating dimensions. As you research which sizes are likely found within your home, here’s what you need to know about standard window sizes, measuring your windows, and how much it costs to install windows. 

What are standard window sizes?

Most types of windows have standard sizes so they can be mass produced and easily fit just about any home. Manufacturers favor common size ranges for windows because they can produce them in bulk, streamline production, and create products for both builders and homeowners (for later replacement). 

Standard window sizes vary based on the type of windows in your home. We break down each type of window and its standard dimensions below.

Common standard window sizes by type

Single-hung and double-hung windows

• Standard widths: 24, 28, 32, 40, 44, or 48 inches 
• Standard heights: 36, 44, 48, 52, 54, 60, 62, or 72 inches 

Single-hung windows have a stationary upper sash and a bottom sash that moves to let in fresh air. In contrast, double-hung windows have both upper and lower sashes that open. These rectangular windows are a convenient choice for homeowners seeking functional, easy-to-maintain windows that provide ample ventilation.  

Casement windows

• Standard widths: 16, 20, 24, 28, 32, 36, 40, 44, or 48 inches
• Standard heights: 24, 36, 48, 54, 60, 72, or 84 inches 

Casement windows are narrow windows that hinge at the side and open by cranking from the side, similar to a door. These windows open very wide, making them a functional choice for ventilation. Casement windows are also excellent for security, as they lock with a latched hook on the inside, making it difficult for someone to break in from the outside. 

Sliding windows

• Standard widths: 36, 48, 60, 72, or 84 inches
• Standard heights: 24, 36, 48, or 60 inches

Sliding windows have a movable window sash that slides horizontally, making them ideal for areas where you can’t easily access a window to push it up, such as over a kitchen sink. These durable windows feature two or three panels and provide an unobstructed view and natural light. 

Picture windows

• Standard widths: 34, 36, 48, 60, or 72 inches
• Standard heights: 36, 48, or 60 inches

Picture windows “frame” an outdoor view. These windows are stationary, with no rails, and provide a clear, unobstructed view of the outside, making them best suited for living rooms or any room that needs more natural light. 

Awning and hopper windows

• Standard widths: 16, 20, 24, 28, 32, 36, 40, 44, or 48 inches
• Standard heights: 24, 36, 48, 54, 60, 72, 84 inches

One of the smaller window types on the market is the awning window, otherwise known as a hopper window, which is rectangular in shape with a hinged top that opens out like an awning. If you’re in an area that frequently gets rain or snow, an awning window lets in fresh air, even during inclement weather, without letting it into your home. 

How window sizes are measured

Windows are measured by height and width. Manufacturers typically list window sizes in a four-digit notation, such as 3030, which indicates a window is 3 feet, 0 inches wide by 3 feet, 0 inches high.

You can either hire a professional to measure your windows for you, or do it yourself at home with a tape measurer. Standard window heights are measured width by height, so start with width. As with any home measurement, you’ll want to complete this process two (ideally three) times to make sure you’ve pulled the correct numbers. 

How to check if the window is square

Before measuring your window, you need to first determine if it’s square (or whether it has 90-degree corners). Take a tape measure to the top right corner of your window, then measure to the bottom right corner and write down the number. Repeat the process with the opposite corner, then compare the numbers. If they’re within 1/4-inch of each other, your window is square. 

How to measure a window’s width

You will want to measure your window’s width in three different places: top, middle and bottom. Place the start of your tape measure on the inside of your left window jamb (this is the white piece that sits on the side of your window’s glass). Begin at the top and stretch the measuring tape to the end of the right jamb. Record that number. Repeat your measurement through the middle of the window, then the bottom. 

You should have three numbers. The smallest number is your width.

How to measure a window’s height

You should measure your window’s height in three places: left, right and middle. Start your tape measure at the bottom of the window (but not the trim, or the piece of material that juts out from the base of the wall that your window sits on). Take it straight to the top of the window and write down the measurement. Repeat with the middle and right side of the window. 

The smallest of those three measurements is your window’s height.

How to measure a window’s rough opening

Measure again as you would for width and height, but measure the opening where a contractor will install the window. Typically, the rough opening is 1/2-inch larger than your window's vertical and horizontal measurements. 

Have a professional double-check your measurements, as the recommended rough opening size varies by window type. Even the slightest error can lead to a poor-fitting window that leaks air, causing your energy bills to rise. 

Lastly, don’t rely on old plans when determining window measurements. Many areas require a building permit for replacing or widening a window, or for adding a new window where none existed before. However, if work was previously done without a permit, it won’t be noted in your home’s old plans. 

Do standard window sizes vary by room?

Window sizes don’t necessarily vary by room, but you’ll find certain window types are more common in particular spaces based on the window’s function and appearance. For example, bedrooms must have a large window that people can escape through in the event of a fire or emergency. The required size varies by location, but is typically at least 20 inches wide by 24 inches tall. 

Most areas don’t require certain windows for kitchens. Still, it’s practical to have windows for ventilation and natural light in this area, so casement, double-hung, garden and sliding windows are commonplace. Similarly, bathrooms don’t usually require specific windows per code, but ventilation is key. You’ll often find bathroom windows that are at least 2 feet wide and 3 feet tall. Popular choices include casement, sliding, double-hung and awning windows. 

As a rule of thumb, these standard window sizes will also vary based on your home’s age. 

When standard window sizes don’t apply

Some homes or windows require custom sizing because of unique window shapes, features, or age—older or historic homes often have window shapes and sizes that were popular back then but aren’t standard today. This is a distinctive part of your home that deserves to be honored with custom replacements, as it’ll maintain your home’s appearance and energy efficiency. 

“A common misconception is that homes use 'standard' window sizes that can be swapped out easily,” said Uri Pearl, owner of Nealon Insulation. “But we see that many older homes have custom or slightly irregular openings, so forcing a standard size can lead to air leaks and trim issues. Accurate measuring and proper fit matter more than finding a "standard" size.”

Specialty windows, such as bay or bow windows, or uniquely shaped windows, such as arch or geometric windows, add visual interest, but don’t come in standard sizes. Instead, these windows are custom-fitted to the outside of your home. Another consideration is any structural changes during home renovations. 

How window size affects cost and installation

Window size impacts cost and installation in several ways. For starters, larger windows require more materials, making them more expensive. 

Custom windows significantly impact the cost of a renovation project because you’ll pay a premium to have them manufactured to your home’s specifications. You’ll also need to factor in the time it takes the manufacturer to make the custom windows. 

As for installation, custom or larger windows come with a higher fee. Some of these windows require creating and framing a new rough opening, which is extra work for the contractor. Others, such as bay and bow windows, require additional home reconstruction during the process, increasing the hours of labor and skill required for the project. 

Bottom line

Standard window sizes are a good starting point when you’re looking for replacement windows. However, accurate measurements and recommendations from a professional window installer are critical to avoid ordering the wrong window size or encountering installation issues. 

Take time to measure your windows carefully, shop around, and then confirm the sizing with a reputable window installer or contractor. 

FAQs 

Are there truly standard window sizes?

No, there aren’t truly standard window sizes, but there are standard window size ranges that many homes incorporate. You can measure your windows at home, but if you’re considering replacing any, you’ll find better peace of mind by ensuring your windows have been measured and confirmed by a professional.

Are replacement windows smaller than the original opening?

Replacement windows are typically slightly smaller than the original opening to ensure a tight fit. Full-frame replacement windows are an option and can improve your home’s energy efficiency and appearance. However, full-frame replacements are more expensive.

Do older homes use nonstandard window sizes?

Older homes frequently use nonstandard window sizes because they feature window sizes and shapes that aren’t popular or standard in today’s market. Another consideration is that older homes typically have larger windows because people relied on them for natural light and airflow before modern technologies emerged.