If you’re ordering custom window screens, it’s critical that you get the measurements correct! Don’t just assume the screen is the same size as your window – window screens are smaller than the window they are to be installed upon. Instead, you will need to supply measurements of the width and height of the finished window screen.

Types of Window Screens:

In order to get the correct measurements, you will need to know if you are measuring for a single hung or a double hung window.

Single hung windows are windows where only one part of the window opens. The screens are sometimes called “half screens” because they only cover the part of the window that opens. That can be the bottom or a side.

Double hung windows are windows where both parts of the window open – either top and bottom or left and right sides. Screens for double hung windows cover the entire window, and usually feature a crossbar in the middle for support.

U-Channels and L-Channels

Regardless of the type of window you have, the screen will generally be fitting into a “U-channel” in the window frame. Screen frames come in different widths. The width of this “u-channel” in your window determines the correct width of the frame needed for your screen. The U-channel is on two sides of your window – either top and bottom or right and left sides.

The “L-Channel” will be on the other two sides. Together, these channels keep your screen in place – preventing it from falling either inside or outside of your house. The U-channel is also where your screen hardware will go.

(Double hung wood windows have a slightly different system, but we’ll get to that later.)

How to measure a single hung window

• From the INSIDE of your house, open your window and note the location of the U-channel.
• Measure the WIDTH of the U-channel first. This will determine your frame width. On a modern single-hung window the width will usually be 5/16”, but it could also be 7/16”, 1/4”, or 3/8”.
• Next, measure the U-channel distance. The depth of the channel is important to getting an accurate measurement, so start with your tape measure IN the deepest part of the U-channel and measure to the upper ridge of the U-channel on the opposite side.*
• Adjust for hardware. If you will need to install any window screen hardware on the u-channel part of the screen, subtract ¼” from your measurement. Otherwise, subtract 1/8”.
• Now get the L-channel measurement. Measure from the innermost part of one L-channel to the outermost ridge of the other L-channel. In case your window isn’t perfectly “square”, take two measurements along different places in the L-channel.
• Adjust the L-channel measurement – Subtract ¼” to 1/8” from the smaller measurement. If your screen will have hardware in the “L” channel (most screens do not) subtract another 1/8”.

How to measure a double hung window

Before you start to measure, from INSIDE your house, lift the bottom half of the window and look at the sides and sill.  If they are wood, follow the instructions for Measuring Wood Window Screens below. Otherwise, follow the instructions for Measuring Non-Wood Window Screens.

Whether aluminum, vinyl or wood, double-hung window screens almost always have a 7/16” frame.

Measuring for Wood Window Screens

• Open the lower window and examine the inside of the window frame. On a wooden window, you should see an inset or “framed” area at the outermost portion of the sill on both sides (and sometimes top and bottom too.) These areas are called “stops” because they “stop” your screen from falling out.
• Measure the width – Measure from the innermost part of one stop to the innermost part of the stop on the opposite side. In case your window isn’t perfectly square, take two measurements – one at the bottom of the window and another in the middle.
• Adjust the width measurement – Subtract ¼” from the smaller of the two measurements.
• Measure the height – Measure from the innermost part of the top stop to the innermost part of the bottom stop opposite it. Take at least two measurements in case your window isn’t perfectly “square” – one from the side and one in the middle.
• Adjust the height measurement – Subtract 1/8” from the smaller of your height measurements.

Measuring for Non-Wood (Aluminum / Vinyl) Window Screens

• Open the lower window from the inside and examine the inside of the window frame. You should see U-channels at the top and bottom, and L-channels on the left and right. This is where your screen will go.
• Measure the L-Channel (width) from the inside of one channel to the inside of the opposite channel. In case your window isn’t perfectly “square”, take two measurements: one from the bottom and one from the center of the window.
• Adjust the L-Channel measurement – Take the shorter of the two measurements and subtract 1/8”.
• Measure the U-Channel (height) – Measure the U-Channel distance from the innermost part of the top U-channel to the top of the top ridge on the bottom U-channel *.
  Again, in case your window isn’t perfectly “square”, take two measurements: one on the right side and one on the left.
• Adjust the U-Channel Measurement – Subtract 1/8” from the smaller measurement. If hardware will be installed, subtract another 1/8”.

*Important note on measuring U-Channels: When measuring u-channel distance, it’s important not to measure between the insides of BOTH channels. To install the screen, you will need to place it in one channel and slide it over the ridge on the other in order to snap it into place. If you measure channel to channel, it will be too big to fit!

Need help with window screens, replacement windows or window / screen repair in the Edmonton area? Call the window pros at Reflect Window and Door for a free estimate!