If you’re thinking about replacing your windows but aren't quite ready to call a contractor, measuring your windows can be a first step to more informed shopping. Let's dig in!

Before you start, you’ll want to gather a tape measure, pen, and paper. It can be useful to have a helper too, especially if you have large windows.

Tip: To help you track dimensions and make other necessary assessments, download one of our measurement guides, like this one for the 400 Series.

You also need to understand a few different parts of a window before taking measurements. These include:

• Jamb: The pieces forming the top and vertical sides of a window or door frame.
• Head (or head jamb): The horizontal piece forming the top of a window or door frame.
• Sill: The horizontal piece forming the bottom of the window or door frame. Here’s the equipment you’ll need:

It’s useful to understand whether or not your windows are in square alignment for several reasons.

• If your windows are square, you might be able to use an insert replacement window, which fits into an existing window frame. This type of replacement window can help you save money, preserve your existing trim, and offer other benefits.
• If your windows are out of square, you’ll need to consider sizing adjustments when ordering new windows. Repairs to the rough opening might be needed as well. For this job, you’ll want an experienced window contractor. Find one in your area through our Certified Contractor program.