How to Measure Your Windows for Impact Replacement

Accurate measurements are critical for impact window replacement. While your dealer will always do a professional measurement, knowing the basics helps you get preliminary quotes and understand the process.

Tools You'll Need

• Tape measure (minimum 25 feet)
• Notepad and pen
• Smartphone camera (to photograph each opening)
• Ladder for upper-story windows

Step-by-Step Measurement Guide

Step 1: Measure the Width

Measure horizontally across the window opening from inside the house:

• Measure at the top, middle, and bottom of the opening
• Record the smallest measurement — this ensures the new window fits
• Measure from jamb to jamb, not frame to frame

Step 2: Measure the Height

Measure vertically from the window sill to the top of the opening:

• Measure at the left, center, and right
• Record the smallest measurement
• Measure from the sill to the head jamb

Step 3: Measure the Depth

Open the window and measure the depth of the window frame from front to back. Impact windows are thicker than standard windows, so adequate depth is important.

Minimum depth required: approximately 3.25 inches for most impact windows.

Step 4: Check for Square

Measure the diagonals of the opening. If the two diagonal measurements differ by more than 0.25 inches, the opening is out of square and may require shimming during installation.

Common Mistakes to Avoid

1. Measuring the glass instead of the opening: Always measure the rough opening, not the visible glass
2. Not accounting for stucco reveals: In Florida masonry construction, measure behind any stucco returns
3. Forgetting to measure all windows: Impact code compliance requires ALL openings to be protected

When to Leave It to the Professionals

While DIY measurements are useful for getting ballpark quotes, the final measurement should always be done by a certified installer. Impact windows are custom-manufactured to exact specifications — even a quarter-inch error can cause problems.

Let Izoah handle the measurements with zero risk. Book your free home assessment — our certified technicians will measure every opening precisely.