Replacing your double hung windows can significantly improve your home’s energy efficiency, comfort, and appearance. However, before you can enjoy these benefits, you need to ensure you’re ordering the correct size windows. Accurate measurements are crucial for a proper fit, optimal performance, and avoiding costly mistakes. This comprehensive guide will walk you through the process of measuring for double hung window replacements, ensuring you get it right the first time.
Understanding Double Hung Windows
Double hung windows are among the most popular window styles in North American homes, featuring two vertically sliding sashes that provide excellent ventilation options. Before measuring for replacement, it’s important to understand the components and terminology associated with these windows.
Key Components of Double Hung Windows
Double hung windows consist of several important parts that you should be familiar with when measuring. The frame surrounds the entire window unit, while the sashes are the movable parts that hold the glass. The sill forms the bottom horizontal part of the frame, and the jambs are the vertical sides of the frame.
Understanding these components helps ensure you’re measuring the correct parts of the window and communicating effectively with window professionals when ordering your replacements.
Replacement Options: Full Frame vs. Insert
Before measuring, you need to determine which type of replacement you’re planning. There are two main approaches to window replacement:
Full frame replacement involves removing the entire existing window down to the rough opening in the wall. This option is ideal when the existing frame is damaged or when you want to change the window size or style.
Insert replacement (also called pocket installation) keeps the existing frame and sill in place, inserting the new window unit within the current frame. This is less invasive and typically more affordable, but requires the existing frame to be in good condition.
Your choice between these options will affect how you measure, so make this decision before proceeding to the measurement steps.
Essential Tools for Accurate Window Measurements
Having the right tools on hand ensures your measurements will be precise. Inaccurate measurements can lead to ill-fitting windows that compromise energy efficiency and may require costly adjustments or replacements.
Required Measuring Equipment
To properly measure for your double hung window replacement, gather these essential tools:
- Steel measuring tape (cloth or plastic tapes can stretch and provide inaccurate readings)
- Notepad and pencil for recording measurements
- Level to check if the existing window is square
- Square tool for checking corner angles
- Smartphone or camera to document the windows
- Flashlight to inspect hidden areas of the window frame
Safety Considerations
Safety should always be a priority when measuring windows, especially for upper floors. Ensure you have a sturdy ladder if measuring windows above ground level. Have someone assist you by holding the ladder and helping with the measuring process when possible. Wear gloves if dealing with old windows that might have splintered wood or sharp edges.
Step-by-Step Measurement Process
Following a systematic approach to measuring your double hung windows will help ensure accuracy. Remember that precision is crucial—even small measurement errors can result in windows that don’t fit properly.
Measuring Width
For width measurements of double hung windows, you’ll need to measure in three different places to account for any irregularities in the frame:
- Measure the width at the top of the window opening
- Measure the width at the middle of the window opening
- Measure the width at the bottom of the window opening
For full frame replacements, measure the distance between the jambs (the vertical sides of the frame) from inside to inside. For insert replacements, measure the width of the pocket opening where the new window will sit.
Always use the smallest of the three measurements when ordering your replacement window. This ensures the new window will fit even at the narrowest point of the opening.
Measuring Height
Similar to width, you’ll need to measure the height in three different locations to account for any variations:
- Measure from the sill to the head jamb on the left side
- Measure from the sill to the head jamb in the center
- Measure from the sill to the head jamb on the right side
For full frame replacements, measure from the top of the sill to the underside of the head jamb. For insert replacements, measure the full height of the pocket opening where the new window will be installed.
Again, use the smallest measurement when ordering to ensure proper fit.
Measuring Depth
Window depth is often overlooked but is crucial for proper installation. Measure the depth of the window jamb from the inside stop to the outside blind stop. For replacement windows, you typically need at least 3¼ inches of depth to accommodate standard double hung replacement units.
If your measurements reveal insufficient depth, consult with a window professional about possible solutions before proceeding with your order.
Checking for Square
Even if your measurements are accurate, windows that aren’t square can cause installation problems. To check if your window opening is square:
- Measure diagonally from the top left corner to the bottom right corner
- Measure diagonally from the top right corner to the bottom left corner
If these measurements differ by more than ¼ inch, your window opening is not square. This doesn’t necessarily prevent replacement, but you should note this information when ordering and discuss it with your window supplier or installer.
Common Measurement Mistakes to Avoid
Even experienced DIYers can make measurement errors that lead to problems with window replacement. Being aware of these common pitfalls can help you avoid costly mistakes.
Measurement Accuracy Issues
Precision matters tremendously when measuring for window replacements. Some common accuracy mistakes include:
Rounding measurements to the nearest inch or half-inch instead of recording exact figures. Window manufacturers work with precise measurements, often to the nearest 1/16 inch.
Measuring from trim to trim instead of jamb to jamb. The trim is not part of the structural window opening and should not be included in your measurements.
Failing to measure in multiple locations. Windows can settle over time, creating openings that aren’t perfectly square or consistent in width or height throughout.
Accounting for Window Operation
Double hung windows need adequate clearance to operate properly. When measuring, consider:
Ensuring sufficient space for both sashes to move freely. If your measurements are too tight, the window may bind when opening or closing.
Checking for obstructions like interior molding, security sensors, or exterior elements that might interfere with window operation.
Verifying that replacement windows will work with existing window treatments like blinds or curtain rods.
Understanding Window Sizing Standards
Window manufacturers have standard sizing conventions that are important to understand when ordering replacements. Knowing these standards can help ensure you get the right product for your needs.
Industry Standard Measurements
Window sizes are typically described using width first, then height. For example, a window listed as 36″ x 60″ is 36 inches wide and 60 inches tall. However, this can vary by manufacturer, so always verify the convention being used.
Most manufacturers produce windows in standard sizes with 4-inch increments for width and height. Custom sizes are available but usually come at a premium price and may have longer lead times.
When ordering replacement windows, manufacturers typically subtract ¼ to ½ inch from your provided measurements to ensure the window will fit in the opening. This is called “deducting for fit” and is standard practice in the industry.
Rough Opening vs. Actual Window Size
The rough opening is the framed opening in the wall where the window will be installed. It’s typically larger than the actual window unit to allow for proper installation and shimming.
For full frame replacements, manufacturers usually require rough opening dimensions. They will then provide a window that’s slightly smaller to allow for proper installation.
For insert replacements, you’ll provide the exact opening measurements where the new window will sit within the existing frame. The manufacturer will then size the replacement unit accordingly.
Recording and Ordering Your Windows
Proper documentation of your measurements is essential for ordering the correct replacement windows. A systematic approach to recording and verifying information can prevent costly errors.
Creating a Measurement Worksheet
Develop a simple worksheet for each window being replaced. Include:
- Window location (e.g., “Master Bedroom North Wall”)
- All width measurements (top, middle, bottom)
- All height measurements (left, center, right)
- Depth measurement
- Diagonal measurements for squareness check
- Notes about any irregularities or special considerations
- Photos of the window from inside and outside
This comprehensive documentation will be invaluable when ordering windows and can help window professionals identify potential installation challenges before they arise.
Double-Checking Before Ordering
Before finalizing your order, take these verification steps:
Re-measure each window to confirm your original measurements. It’s best to do this on a different day to ensure consistency.
Have a second person independently measure the windows and compare results. Discrepancies should be investigated and resolved.
Review manufacturer specifications to ensure the windows you’re ordering will fit your openings and meet your needs for energy efficiency, style, and function.
Professional Assistance vs. DIY Measuring
While measuring for replacement windows is something homeowners can do themselves, there are situations where professional assistance may be beneficial or necessary.
When to Call a Professional
Consider professional measuring services in these scenarios:
For homes with unusual window configurations, extremely old windows, or significant structural issues around window openings.
When planning to change window styles or sizes, which may require structural modifications to the wall.
If you’re replacing many windows at once, where the cost of a measuring error would be multiplied across multiple units.
Most window retailers and installation companies offer professional measuring services, often at no charge if you purchase windows through them. This service typically includes a guarantee that the windows will fit properly.
Benefits of Professional Measurements
Professional window measurers bring expertise and experience that can be valuable:
They can identify potential installation challenges that might not be obvious to homeowners.
Many professionals use digital measuring tools that provide extremely accurate measurements.
Professional measurements often come with a fit guarantee, meaning the company will take responsibility if the windows don’t fit properly.
They can provide advice on the best replacement options based on your specific situation and home configuration.
Whether you choose to measure yourself or hire a professional, accurate measurements are the foundation of a successful double hung window replacement project. Taking the time to get this crucial first step right will ensure your new windows perform efficiently and look beautiful for years to come.
