You've made the decision to upgrade your windows to something more energy efficient and low maintenance like fiberglass windows. It is best to measure your windows properly the first time around to prevent problems when fitting the new windows into the opening. The following is a basic guide how you can measure your windows to get as close as possible to your frame's dimensions. This guide will be helpful when providing the fiberglass window manufacturer with the correct dimensions of your windows.
Measure from the Inside
When measuring your windows for replacement, it is best to measure from the inside of the house. Start by measuring the frame width, followed by the frame height. If your casing is a standard size, measure about halfway from the middle of the casing, to the other end, halfway into the casing as well. If the casing is wider than standard, measure from about an inch into the casing, closer to the window frame.
To assure consistency in width and height, you can measure the width and height at three different points of the window: left, centre and right, and or top, centre and bottom. The smallest of the three measurements will be the right width/height.
Measuring the Window's Depth
The jamb extension is an additional component to the window from the interior lengthening the depth of the window. This is relevant for door frames as well. The depth of the window needs to be measured to determine what size jamb extension will be needed. In the case of drywall return, this step can be overlooked when sending dimensions to the window manufacturer. The depth will vary depending on the wall thickness of your home. Usually older homes tend to have a thicker wall than homes that have been built from 1970 and onward.
A great tip to consider when measuring your windows is to always sketch out the window and label its location (Bedroom, bathroom, etc) along with its orientation. This causes less confusion later when providing sizes to the window manufacturer.