Tools Needed: A tape measure, pencil and a copy of our measurement worksheet. Accurate Measurements are the key to quality installations. When you specify a vinyl replacement window, it is made to fit the particular opening and it is important to correctly measure the opening. There are three critical measurements involved:

Width: This is the measurement that is given first when ordering a window. Because the inside stops and parting stops are removed, the width must be measured from jamb to jamb as shown. Measure at the top, middle, and bottom and use the smallest dimension.

Height: The height of the window is taken from the sill (from the point against the stool) to the header (at the point against the inside stop) as shown. Measure at the left, middle, and right and use the smallest dimension.

Square: Because some openings have become out-of-square over the years, it is important that the squareness of the opening be accurately measured. Measure the diagonals (upper left to lower right, and upper right to lower left) as accurately as possible from a point inside the stool to a point against the inside stop at the header. Record the two dimensions. If they are roughly equal, the opening can be assumed to be square. If they are not, then it is possible that the opening is out-of-square enough to cause the new window to be forced into an out-of-square condition during installation.