Many pros recommend subtracting 1/8" (about 3mm) from your final width and height to provide "fitting tolerance" so the glass isn't too tight to install.
Do not measure the old broken glass, as it may be chipped or incorrectly sized. Measure the frame opening where the glass sits. buy window glass online
Record the smallest of your three width and height measurements to ensure the new pane will fit into the frame. Many pros recommend subtracting 1/8" (about 3mm) from