How to Measure a Window for Replacement Guide for Eastern Washington Homeowners & Contractors

Understanding Window Measurement Basics for Eastern Washington Homes

Measuring a window for replacement might seem straightforward, but getting it right the first time is crucial for a successful installation. After serving Eastern Washington homeowners since 1979, we’ve seen countless measurement mistakes that could have been easily avoided with the right knowledge. Whether you’re dealing with a century-old farmhouse in Kettle Falls or a modern home in Airway Heights, accurate measurements are the foundation of any window replacement project.

The key principle is simple: measure the existing window frame opening, not the glass or exterior trim. You’ll need to record four critical dimensions from inside your home: width, height, depth, and check for squareness. Always use the smallest measurement from multiple points and order your replacement window 1/8 inch smaller than these dimensions to ensure proper fit and installation.

In Eastern Washington’s challenging climate—where temperatures can plummet to -20°F in winter and soar above 100°F in summer—precision matters even more. Our extreme temperature swings cause significant expansion and contraction, making proper sizing and shimming essential for long-term performance.

Essential Tools for Accurate Measurements

Before you start, gather these tools: a quality 25-foot tape measure, level, square, pencil, and paper or smartphone for recording measurements. A helper makes the job easier, especially for larger windows. Take photos as you work—they’re invaluable when discussing your project with window suppliers or contractors.

Step-by-Step Measurement Process

Measuring Width: The Three-Point Method

Start by measuring the width of your window opening at three different heights: near the top, center, and bottom. Place your tape measure between the left and right jambs (the vertical sides of the window frame), not against any trim or stops. In older Spokane area homes, these measurements often vary significantly due to settling—it’s not uncommon to see differences of 1/4 inch or more between the top and bottom measurements.

Record all three measurements and use the smallest one for ordering. For example, if your measurements are 35-1/4″, 35-1/8″, and 35-3/8″, order based on the 35-1/8″ measurement. This ensures your new window will fit through the tightest point in the opening.

Measuring Height: Top to Bottom Precision

Next, measure the height at three points: left side, center, and right side of the window opening. Measure from the head jamb (top horizontal piece) down to the sill (bottom horizontal piece). Again, ignore any trim or interior stops—you want the actual frame opening dimensions.

In our experience serving Colville and surrounding areas, homes built on the region’s clay-heavy soils often show more height variation than width variation due to differential settling. Don’t be surprised if these measurements also differ by 1/8 to 1/4 inch.

Checking for Square: The Diagonal Test

Measure both diagonals of your window opening from corner to corner. If your window is perfectly square, these measurements should be identical. However, a difference of up to 1/4 inch is generally acceptable for most replacement windows. Anything beyond that may require professional adjustment of the frame or selection of windows specifically designed for out-of-square openings.

This step is particularly important in Eastern Washington, where seismic activity and soil movement can shift window frames over time. We’ve seen many older homes in the Kettle Falls area where original settling created significantly out-of-square openings.

Measuring Depth: Ensuring Adequate Space

Measure the depth of your window opening from the interior window stop to the exterior stop. Most replacement windows require a minimum depth of 3-1/4 inches, though some high-performance windows designed for our climate may need more. If your opening is too shallow, you may need to consider a different window style or have the opening modified.

Eastern Washington Climate Considerations

Our region’s unique climate demands special attention to window selection and measurement accuracy. The extreme temperature variations between our cold winters and hot summers create significant expansion and contraction forces that can stress improperly fitted windows.

Energy Performance Requirements

When measuring for replacement windows in Eastern Washington, consider that building codes now require windows with specific energy performance ratings. Look for windows with a U-factor of 0.30 or lower and a Solar Heat Gain Coefficient (SHGC) between 0.25 and 0.40. These ratings ensure your windows can handle our climate extremes while keeping energy costs reasonable.

The measurement process becomes more critical with high-performance windows because many feature thicker frames and multiple panes. Triple-pane windows, which are increasingly popular in our area, require precise measurements to ensure the additional weight is properly supported.

Dealing with Seasonal Movement

In Eastern Washington, measure your windows during moderate weather when possible. Extreme cold can cause frames to contract, while summer heat causes expansion. Measuring during spring or fall gives you the most representative dimensions for year-round performance.

The rocky, clay-rich soils common around Spokane and extending north to our Colville location can cause ongoing settling that affects window measurements over time. If your home is experiencing active settling, consider having measurements verified by a professional before ordering expensive replacement windows.

Common Measurement Mistakes and How to Avoid Them

Measuring Trim Instead of Frame

The most frequent mistake we see is homeowners measuring the decorative trim around their windows instead of the actual frame opening. This can result in ordering windows that are too large by several inches. Always measure the structural frame members—the jambs, head, and sill that actually hold the window.

Single-Point Measurements

Taking just one measurement for width and height might work in a perfect world, but real-world window openings are rarely perfectly uniform. This is especially true in Eastern Washington’s older homes, where decades of freeze-thaw cycles and settling have shifted frames. Always take multiple measurements and use the smallest ones.

Ignoring Depth Requirements

Failing to measure depth is a costly oversight. Modern energy-efficient windows often have deeper frames than older single-pane windows. If your existing opening lacks adequate depth, you’ll need to modify the opening or select a different window style—both expensive surprises that proper initial measurement can prevent.

Forgetting About Operating Clearance

Don’t forget to consider how your windows operate. Casement windows that swing outward need clearance from exterior obstacles like decks or landscaping. Double-hung windows need interior clearance for the sash to slide properly. Factor these operational requirements into your measurement process.

When to DIY vs. Hire a Professional

Suitable DIY Scenarios

Simple pocket replacements in structurally sound, rectangular openings are often good DIY projects for handy homeowners. If your measurements show the frame is reasonably square (diagonals within 1/4 inch) and you’re replacing like-with-like (double-hung for double-hung, for example), you can likely handle the measurement and installation yourself.

Call in the Professionals

Consider professional measurement and installation for:

• Windows that are significantly out of square
• Multi-story installations
• Rotted or damaged frames (common in areas with poor drainage)
• Unusual window shapes or sizes
• Full-frame replacements requiring exterior work
• Homes built before 1978 (potential lead paint concerns)

In our experience, professional contractors familiar with Eastern Washington’s building practices can spot potential issues that might not be obvious to homeowners. They also have specialized tools for dealing with out-of-square openings and can ensure compliance with local building codes.

Cost Considerations

Professional window installation in the Spokane area typically ranges from $300 to $1,200 per window, including materials. Factors affecting cost include window size, frame material, energy performance features, and installation complexity. Rural locations like Kettle Falls may see slightly higher costs due to travel time and limited contractor availability.

DIY installation can save 20-50% on labor costs, but factor in the value of warranties and professional expertise. Many window manufacturers offer better warranties on professionally installed products, which can be significant given our harsh climate conditions.

Selecting the Right Windows for Eastern Washington

Frame Materials for Our Climate

Vinyl windows offer excellent value and low maintenance, making them popular throughout Eastern Washington. They handle our temperature extremes well and won’t rot or corrode. Fiberglass frames are stronger and more dimensionally stable, important for larger windows or areas with significant soil movement.

Wood-clad windows provide beautiful interior aesthetics with weather-resistant exteriors, though they require more maintenance and precise measurement due to their weight and construction requirements.

Glass Performance Features

In Eastern Washington’s climate, dual or triple-pane windows with Low-E coatings and argon gas fills are essential. These features help windows perform in temperatures from -20°F to over 100°F while reducing energy costs. The additional thickness of high-performance glass affects frame dimensions, making accurate measurement even more critical.

Consider impact-resistant glass if you’re in an area prone to hail or high winds. Some locations in Eastern Washington experience severe weather that can damage standard glass, making the upgrade worthwhile for long-term protection.

Final Measurement Tips and Best Practices

Always measure twice and order once. Double-check your measurements before placing your order, and don’t hesitate to have a second person verify critical dimensions. Keep detailed records of all measurements, including photos showing where each measurement was taken.

Consider the installation method when measuring. Pocket replacements (where the new window fits into the existing frame) require different measurements than full-frame replacements (where the entire window and frame are replaced). Make sure you’re measuring for the correct installation type.

Factor in your home’s age and construction methods. Homes built in different eras used different standards and materials. A house from the 1950s likely has different framing than one built in the 1990s, affecting measurement requirements and installation approaches.

Don’t rush the measurement process. Taking accurate measurements is far less expensive than ordering the wrong size windows or dealing with installation problems later. Plan for an hour or more to properly measure a typical window, especially if you’re learning the process.

Ready to tackle your window replacement project? At Builders Supply & Home Center, we stock a complete selection of energy-efficient replacement windows suitable for Eastern Washington’s demanding climate. Our knowledgeable staff at our Airway Heights, Colville, and Kettle Falls locations can help you select the right windows and provide guidance on measurement and installation. Visit us online at bldrsupply.epicor-inet.com/departments to explore our window selection and get started on your project today.