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How to Measure for Replacement Windows (2024)

By Tamara Jude Updated July 24, 2024

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A window upgrade project allows a homeowner to refresh their home’s curb appeal, improve their energy efficiency, and add new life to their interiors. When shopping for the best replacement windows, you need the exact measurements of each window to find the perfect option. 

Having accurate measurements ensures your final installation results in a tight, draft-free fit. We’ll explain how to measure for replacement windows to ensure your next home improvement project goes smoothly.

 

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Why You Should Measure Your Windows

If you’re considering replacement windows, you need measurements to ensure a proper fit. Having precise measurements on hand will make your shopping experience easier, whether you’re visiting an in-store location or meeting with a windows company virtually. Installers can provide a more accurate cost estimate for window replacement if you have proper measurements.  

 

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How to Measure Windows for Replacement Windows

Measuring windows doesn’t require any special know-how. You’ll need a tape measure, a writing tool, and paper to record your measurements. If you need to replace multiple windows in different rooms, label each page with the room name and window location. For example, use labels such as “living room, left double-hung window” or “kitchen, sliding window over the sink.” You could also record the measurements in a note-taking app to keep them handy. 

Below are step-by-step instructions on how to get measurements for your new replacement windows. 

1. Check Windows for Squares

You’ll begin your measuring by determining if your current windows are squares, meaning each corner has a 90-degree angle. Although standard window sizes vary, you want to confirm if your new replacement windows need 90-degree angles to match. 

To begin the process, take measurements from inside your home. Follow the below instructions:

• Hold the tape measure in the corner of the top right side of the window where the vertical and horizontal trim boards meet. 
• Stretch the measuring tape diagonally to the bottom left corner where the trim boards meet. 
• Record these measurements on a sheet of paper or your phone.
• Repeat the same procedure and measure from the top left corner to the bottom right corner. 
• Record this second measurement.

Next, compare your measurements. If those numbers are within 1/4 inch of each other, a standard replacement window will fit securely in the opening. However, if the two measurements are greater than 1/4 inch, you’ll need to select an alternative window replacement. You can either replace your window frame or choose a new construction window instead of a replacement window.

2. Measure the Window Width

Standard windows require width and height measurements for the perfect fit. You’ll take width measurements in three places: the top, the middle, and the bottom of the existing window. Make sure to take these measurements inside the window jambs on both sides. The jamb is the main vertical section that forms the outside of the window frame. 

Follow the below instructions to record the width of the window:

• With the window closed, measure between the two jambs at the top of the window. 
• To measure the middle of the window, open the window and measure between the jambs as close to the middle as possible. 
• Keep the window open, and measure the bottom of the window between the right and left jamb. 

Record each measurement, and circle or highlight the smallest measurement. That measurement is the window opening width. 

3. Measure the Window Height

To determine the height of the window, you’ll need three measurements: on the left side, in the middle, and on the right side. You’ll measure the head jamb (header)—the top horizontal board right above the window—to the bottom window sill. The sill is where the window sash (the movable part of the window that holds the glass) sits when the window is closed. The sill shouldn’t be confused with the window stool, the bottom trim that extends into the room. 

Take your three measurements and record them. Circle or highlight the shortest measurement. This number represents the window opening height.

4. Measure the Window Depth

In most homes, window depth isn’t required for replacement window measurements. In rare cases, the window depth could be too narrow for a replacement window. To find the depth, open the window. Next, measure the sill space from the front to the back of the trim. This space should be, at minimum, 3¼ inches to accommodate a replacement window. 

5. Measure for Window Screens

There are two options to measure window screens. If you plan to replace your current screen with a new one, use the width and height of that screen for a perfect match. 

However, if you plan on adding a screen and your current window doesn’t have one, follow these steps to determine the right size:

• Measure the distance between the horizontal screen channels within the window frame. 
• Subtract 1/8 inch from that measurement. This is the width of the screen. 
• Next, open the window and find the height by measuring from the “lip” to the window sash. The “lip” is the ridge that holds the screen in place. 
• Add 1/8 inch to this measurement. This is the height of the screen.

6. Measure for Storm Windows

The steps for measuring storm windows are the same for double- and single-hung windows. Follow the below steps to measure for storm windows:

• For the height, measure from the sill to the inside of the trim at the top of the window. Measure the left, middle, and right sides. The shortest measurement is the height. 
• For the width, measure from the left jamb in the inside trim to the right jamb in the inside trim. The smallest measurement is the width. 
• Use the shortest width and height measurements for your order.

7. Finalize Your Measurements

Once you have compiled your window measurements, it’s time to determine the final size for your replacements. Using those circled measurements (the shortest measurements for height and width), round down to the nearest 1/8 inch. If the original measurements are in 1/8-inch increments already, don’t make any adjustments. These measurements will serve as your guide to ordering replacement windows.

It’s important to measure each window individually. Do not rely on your measurements for one window to match the dimension of another. Neglecting to measure each window could lead to faulty installation, leaks, or crooked windows. Measurements are key to a successful installation, so take the time to measure each window carefully. 

8. Order Your Replacement Windows

Take your finalized measurements to the window company to place your order. You could also purchase your windows from a hardware store. Remember that windows in these stores might not perfectly match your dimension. We recommend ordering custom windows designed for your measurements to ensure the best fit. Some window installers only offer custom-built windows for better installation results.

 

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Professional vs. DIY Window Measurement

Window measurement requires precise dimensions and calculations to determine the right size for your home. Although the task isn’t difficult, some homeowners second guess their measuring skills. If you’re uncomfortable with measuring windows, have a professional handle the task instead. 

Many professional window installers will visit your home for a free consultation and quote. During their visit, the representative will review your current windows, check their condition, and take measurements. Based on this information, they will calculate a quote for your project, including the cost of your new windows, any customizations, warranty information, and final pricing. Some companies send a separate technician to measure your windows before placing the order for your new windows. 

Choosing a professional to measure your windows is the best option for a more complicated installation. For example, finding the right measurement for a bow or bay window might be daunting for the average homeowner. Certain types of windows, such as awning or casement windows, require additional planning because they open externally. You’ll need to account for the space around the windows to prevent issues with their functionality. In these cases, a professional installer could better assess your home’s design and recommend the best placements for these windows.

 

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Our Recommendation

Measuring your windows helps you prepare for your replacement window project and find the perfect option for your home. You’ll avoid drafty windows, crooked installations, and high energy bills. If you are uncomfortable taking measurements yourself, we recommend contacting your potential windows installer for assistance. 

Whether you’re looking to repair your current windows or update your home’s curb appeal, taking precise measurements will help you achieve a successful home improvement project.

 

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