How to Measure for Pella Replacement Windows

Close the existing window. Stretch the tape measure horizontally across the width of the window opening, at the top. Measure from the two opposing sides of the window jamb (the flat spans of wood framing the sides of the window opening), making sure you're measuring from the farthest part outward. The tape measure should be just behind the vertical piece trim that borders the front of the lower window sash, in the space where the sash would be if you opened the window.

Write down the measurement on a piece of paper.

Move the tape measure to the middle of the lower sash. Measure across as before. Write down the measurement.

Raise the window. Measure the width at the bottom of the opening, in the space where the sash was when it was down. Write down the measurement.

Take the smallest of the three measurements and subtract one-half inch. For example: If your measurements were 31 3/4 inches, 31 7/8 inches and 32 inches, your final number would be 31 1/4 inches. Write down and circle your final number. This is the adjusted width to give to your window manufacturer when ordering your window.

Open the bottom sash of the window halfway, so the sash is in the middle of the window opening and you can access the horizontal top and bottom areas of the opening. Stretch your tape measure from the top of the opening down to the window bottom on one side. Write down the number.

Take two more vertical measurements: one at the middle of the opening and the other from the opposite side of where you took the first one. Pick the smallest of the three measurements and subtract one-half inch. This is the height figure to use in ordering the window.