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How to Measure for Replacement Windows

Beth Asaff
Measuring tape

Learning how to measure for replacement windows can help you get your project done right the first time. Proper measurements are the key to success in any home improvement job, and installing replacement windows is no different.

Replacing Your Windows

One of the top reasons for replacing windows in any home is the leaks and drafts that can occur from old and poorly fitted windows. While newer windows are frequently more energy efficient and easier to clean, the reason most people finally make the switch has more to do with a cold draft blowing their curtains while the windows are shut.

What makes these old windows so drafty is in part a poor fit with the frame. Wood can swell, shrink and crack over time making old fashioned windows stick, rattle and fit improperly in their frames. To truly make sure your new replacement windows are going to be air-tight once installed, you will need to order the windows to fit the exact measurements of your frame.

Proper Measurements

Before any home improvement should be undertaken in your home, proper measurements should always be taken and written down. Measurements can help ensure several things including:

  • That the correct amount of material is ordered
  • The correct size of material is ordered
  • Custom parts can be made to order if standard sizes will not fit
  • Materials can be cut to size properly

When measuring anything for the home, including replacement windows, be sure to remember the following tips:

  • Take the same measurement from two or three areas. Houses can shift and materials can warp, taking two or three measurements will give you the most accurate picture of the job.
  • Draw a small diagram of the unit and label each section with measurements. This will help you remember exactly what measurement corresponds to what part when you are placing an order.
  • Take each measurement twice. If the numbers differ when taken in the same spot, measure a third time for accuracy.

Measuring for Replacement Windows

Before you can learn how to measure for replacement windows, you're going to have to get familiar with your window frame. Since every window is slightly different, and whether your home has its original windows or replacement windows already can affect how it looks, taking the time to learn where each part is located can make taking measurements easier.

Raise up your window as far as it can go and examine the interior of the frame. There should be several areas on each side that come toward you and some that recede. The areas jutting out are called stops and you should have three: the inside stop on the inside of the window, the parting stop just behind the window and the outside stop at the farthest point. If you have had replacement windows in this frame in the past, the parting stop is likely covered in a jamb liner of aluminum or plastic.

Take a look at the sill of your window next. Many windows have a sill which slopes down as it comes inside. You will make your measurement for the height of the window from the back, or highest point of the sill.

Take your first window measurement on the inside of the jamb, between the inside and parting stops from left to right to get the window's width. Subtract 1/4 inch from your measurement to find the size of width required for your replacement window.

Measure the height from the back of the sill to the jamb, or depression at the top of the window frame. Subtract 1/4 inch from this measurement as well before ordering.

Measure the depth of the window by measuring the distance between the outside and inside stops. Replacement windows require a minimum of 3 1/4 inches of depth for this area.

Once your measurements have been taken, you can talk to a contractor about ordering and installing the windows for you or you can order the windows to install them yourself.

Learning how to measure for replacement windows can help ensure your project goes smoothly and your new windows fit tightly. Take proper measurements of each window you are replacing in your home and know that your new windows will be exactly the right fit.

How to Measure for Replacement Windows