If you’ve been thinking about replacing your windows, you may have wondered: Do I need to measure first? The short answer is, most of the time, yes. Accurate measurements are essential to getting windows that fit, seal properly, and perform the way they should. The longer answer is that how you measure (and who does it) makes a big difference. This guide will walk you through the process step by step. But here’s the thing: if you choose Renewal by Andersen, our factory-trained specialists handle all of this for you, and we guarantee the fit.
Why Accurate Window Measurements Matter
An improperly sized window can cause drafts, water infiltration, and structural damage over time. Windows that are even slightly off can be difficult to install, create gaps that hurt energy efficiency, or require costly alterations to the rough opening. Getting it right from the start saves time, money and headaches down the road.
What You’ll Need (DIY Measurement Guide)
Before you start, gather:
- A steel measuring tape (cloth tapes can stretch and give inaccurate readings)
- A notepad or your phone to record measurements
- A level (to check for any bowing or unevenness)
Step 1: Measure the Width
Open the window and measure the width of the opening from inside the house. Measure at three points: the top, middle, and bottom of the opening. Use the smallest of the three measurements. This ensures the window will fit even if the frame has shifted or bowed over time.
Record this as your width measurement.
Step 2: Measure the Height
Measure the height of the opening from the window sill to the top of the frame. Again, take three measurements: left side, center, and right side. Use the smallest number.
Record this as your height measurement.
Step 3: Check for Square
Use a level or measure diagonally from corner to corner. If both diagonal measurements are equal, the opening is square. If they’re not, you may need a custom-sized window or a contractor who can adjust the rough opening. This adds cost and complexity.
Step 4: Check the Depth
Measure the depth of the window frame (from the interior wall to the exterior). This matters for the type of window you can install.
Step 5: Account for the Installation Method
There are two main types of replacement installations:
- Insert (pocket) replacement: The new window slides into the existing frame. Your measurements above apply here.
- Full-frame replacement: The entire frame is removed down to the rough opening. Measurements will differ, and the project becomes more involved.
- If you’re unsure which type you need, it’s worth having a professional assess your current frames for rot, damage, or structural issues before you order.
Common Measurement Mistakes to Avoid
- Measuring only once. Always take three measurements per dimension and use the smallest.
- Using a cloth tape measure. Steel only.
- Forgetting to check for square. Out-of-square openings need special attention.
- Measuring from the outside. Always measure from inside the home.
- Not accounting for trim. Interior and exterior trim isn’t part of the rough opening, don’t include it.
When You Work With Renewal by Andersen of Greater Wisconsin, You Don’t Measure at All
Here’s what makes working with Renewal by Andersen different from buying windows at a home improvement store: we send a factory-trained specialist to your home who takes precise measurements of every window before anything is ordered.
Our team measures each opening multiple times, checks for level and square, evaluates the condition of your existing frames, and determines the right installation approach for your home. We then build your windows to those exact specs using our proprietary Fibrex® material, a composite that’s stronger and more energy-efficient than vinyl.
And we back every installation with our Transferable Limited Warranty, which covers the product and the installation. If there’s ever a fit issue, it’s on us.
Ready to Skip the Tape Measure?
You don’t need to measure your windows or worry about getting the specs right. That’s our job. Schedule a free in-home consultation with Renewal by Andersen and let our specialists do the measuring and the rest.
