How to Get an Accurate Measurement for a Window Pane

Measure the depth of each pane. For example, if your window is double-hung, measure the front-to-back width of the outermost pane and the pane that is recessed. Mark the results "outward depth" and "recessed depth" on paper.

Measure the pane's inner width and height. Measure from inside edge to inside edge for both. Window panes might not have an even width or height. Measure from three points for the width: top, middle and bottom. Write down all three results. Measure from the right side, left side and middle part for the height. Write down all three results. Mark the smallest width result "inside width" and the largest width result "inside height" on the paper.

Measure outside pane width and height. Measure top, middle and bottom for outside width and the left side, right side and middle for the height. Write down all measurements. Mark the largest measurement for the width "outside width" and the largest measurement for the height "outside height" on the paper.

Measure the inside of the pane frame at all four corners if you're replacing glass only. Write down all four measurements. Subtract one-eighth inch from the measurements to allow for the expansion of the glass during temperature changes.