Homeowners: How to Measure Windows for Replacement

Measuring your windows accurately is essential for choosing the right replacement. This process can be broken down into three simple steps: measuring the rough opening for width, height, and depth.

What Is a Rough Opening?

The rough opening is the framed space in the wall where your window will be installed. It’s slightly larger than the actual window size to allow for adjustments during installation. Precise measurements are crucial to ensure a secure fit. Below, we’ll guide you through the process with illustrations to help visualize where and how to measure.

Step 1: Measure the Rough Opening Width

How to measure:

1. Using a tape measure, measure horizontally from one side jamb (vertical frame edge) to the other at three points:
   • Top
   • Middle
   • Bottom
2. Write down all three measurements.
3. Use the smallest number—this is your rough opening width.

💡 Tip: Always list window measurements as width × height when purchasing replacements.

Step 2: Measure the Rough Opening Height

How to measure:

1. Measure vertically from the head jamb (top of the frame) to the window sill at three points:
   • Left side
   • Center
   • Right side
2. Record all three measurements.
3. Use the smallest measurement—this is your rough opening height.

💡 Tip: If your window sill is sloped, measure from the highest point where the window sits.

Step 3: Measure the Window Depth

Why depth matters: Some windows may be too deep for the opening, so it’s essential to check this dimension.

How to measure:

1. Open the window (if possible) and measure from the inside edge of the frame to the outside edge at multiple points.
2. Record all measurements and use the smallest depth to ensure a proper fit.

If your window can’t be opened:

• Measure the depth on each side of the glass.
• Add those measurements together along with the glass pane thickness (typically 1/8 inch or 3mm).

Why Accurate Window Measurements Matter

Incorrect window sizing can lead to several issues:

• Energy efficiency loss: Gaps allow air leakage, increasing energy bills.
• Difficult installation: A poorly sized window may require costly modifications.
• Structural problems: Improperly fitted windows can cause alignment and sealing issues.

Taking accurate measurements from the start will save you time, effort, and money in the long run.