How to Measure RV Windows for Replacement

To measure RV windows for replacement, remove the existing window, measure the rough opening width and height to the nearest 1/16", record sidewall thickness, and determine the corner radius. These measurements ensure the replacement window fits correctly and installs without modification.

Knowing how to measure RV windows is the most important step before ordering replacement glass or a new frame. Even small measurement errors can lead to fitment issues, delays, and unnecessary returns. Accurate dimensions help ensure your new window aligns with the wall opening, seals properly, and installs cleanly.

This guide explains how to measure RV windows, understand RV window sizes, and prepare to order replacement components or contact Lippert’s glass experts.

• Why Accurate Measurements Matter Before Ordering Replacement Windows
• Tools Needed to Measure RV Windows
• Step 1: Remove the Existing Window
• Step 2: Measure the Rough Opening (Not the Old Window)
• Step 3: Measure Sidewall Thickness
• Step 4: Measure Corner Radius
• Understanding RV Window Sizes
• Common Mistakes When Measuring RV Windows
• What to Do After You Measure
• Ordering Replacement Windows from Lippert
• FAQs About Measuring RV Windows & Choosing the Right Size

Accurate measurements prevent installation issues, ensure a proper seal, and help match the replacement window to the RV’s rough opening rather than the old frame.

Replacement windows are sized based on the rough opening in the wall, not the old window frame. Measuring incorrectly can result in gaps, poor sealing, or a window that simply won’t fit.

Manufacturers design replacement windows slightly smaller than the rough opening to allow installation and sealing. Measuring carefully reduces installation complications and ensures compatibility with wall thickness and corner radius.

Accurate measurements also help determine whether you need a standard replacement or a custom solution.

Before starting, gather:

• Screw gun
• Tape measure (capable of 1/16" increments)

• Putty knife

These basic tools allow you to safely remove the old window and measure the wall opening without damaging exterior surfaces or interior trim.

Before ordering replacement glass or a full window assembly, it’s important to follow a consistent, accurate process. These steps walk through how to measure RV windows correctly by focusing on the rough opening, wall construction, and corner details that determine proper fit. Taking the time to measure carefully helps avoid delays, reorders, and installation issues.

Start inside the RV:

1. Remove screws around the interior window frame. Larger windows may have 12–20 or more screws.

2. Remove the trim ring and set it aside.

3. Push the window outward from inside the RV.

Have a second person hold the window from the outside to prevent it from falling. If the window is sealed tightly, slide a putty knife beneath the exterior flange and work around the perimeter until it releases.

Take care not to damage exterior paint, decals, or sidewall material during removal.

Measure the wall opening itself — width and height — not the old window. Record dimensions to the nearest 1/16" for accurate ordering.

This is the most important step in how to measure RV windows. Measure the rough opening in the sidewall:

• Measure width and height directly from the opening

• Record to the nearest 1/16"

• Measure twice to confirm accuracy

Replacement windows are built to fit this opening, not the removed window. The rough opening determines final sizing and compatibility. When measuring, accuracy matters because even small discrepancies can affect installation and sealing.

For irregular window shapes:

• Parallelogram or trapezoid openings require six measurements

• Use masking tape to extend measurement lines beyond corner radiuses

• Measure from intersection points rather than curves

This ensures your dimensions reflect the true structural opening.

Measure from the exterior wall surface to the interior wall surface to determine sidewall thickness and trim compatibility.

Sidewall thickness affects trim ring fit and installation depth.

Measure:

• From exterior wall surface

• To interior wall surface

• Excluding the window frame

Typical RV wall thickness ranges from about 1-1/4" to 2-1/2". Matching this dimension ensures the replacement window clamps properly and seals against the wall.

Match the corner curve of the rough opening using a radius template or compass to ensure proper window alignment.

Many RV windows have rounded corners. Most use:

• 2.5" radius

• 3" radius

Do not assume the size. Measure each opening.

To determine radius:

• Use a printed radius template or compass

• Hold it against the opening corner

• Match the curve precisely

If your window has square or mitered corners, this step is not required.

RV window sizes vary widely, and replacements are typically based on rough opening dimensions rather than standardized window frame measurements.

Unlike residential windows, RV window sizes are not universally standardized. There are dozens of commonly sold dimensions across manufacturers and vehicle types.

Some of the most frequently seen RV window sizes include:

• 12×22

• 48×22

• 14×16

• 30×20

• 24×15

• 24×22

• 24×24

• 18×18

Widths commonly cluster around 12", 24", 14", and 30", while 22" is one of the most common heights. Because RV window sizes vary so much, accurate measurement is the only reliable way to ensure the correct replacement.

The most common mistakes include measuring the old frame instead of the rough opening, skipping radius measurements, and rounding dimensions.

Avoid these issues:

• Measuring the existing window instead of the wall opening

• Guessing corner radius

• Rounding measurements

• Skipping sidewall thickness

• Measuring only once

Double-checking each dimension reduces ordering errors and installation delays.

Use your measurements to order a replacement window or contact a glass specialist to confirm sizing and compatibility.

After documenting your dimensions:

1. Confirm width and height of the rough opening

2. Verify sidewall thickness

3. Confirm corner radius

4. Compare against available RV window sizes

You can then move forward with ordering replacement glass, a full window assembly, or a custom solution.

Replacement windows are typically built slightly smaller than the opening to allow installation and sealing clearance, which is why measurement accuracy is essential.

Provide rough opening measurements, wall thickness, and radius details to Lippert’s glass team to identify compatible replacement windows.

Once you know how to measure RV windows, the next step is ordering.

Have these details ready:

• Rough opening width and height

• Sidewall thickness

• Corner radius

• Window type (slider, fixed, vented, etc.)

These measurements help identify the right replacement window or determine if a custom solution is required.

Contact Lippert’s glass experts to:

• Confirm measurements

• Identify compatible products

• Discuss replacement options

• Request assistance before ordering