You ll need to do the following.
How to measure for exterior storm windows.
Insert the storm windows.
Measuring for a storm window replacement can be a frustrating task.
Measure opening width at three locations top center bottom measure opening height at three locations right center left round the narrowest width and the shortest height down to the nearest 1 16 and provide these dimensions when ordering.
Determine if window casing is eastern see 4a or western see 4b.
Step 1 measure width begin by measuring the width of the window inside of the frame.
Alternatively you may measure an existing storm window and order the window tip to tip.
When ordering give width first then height.
Insert your storm windows into the opening and tightly against the window sill.
If you find yourself with this project here is a quick guide to help you through the measuring process.
If oriel give the measurement from step 3.
Make sure position the window straight.