Each manufacturer has a different shape to their ballistic panels, so the answer to this can vary. Though this is not specific, generic panel sizing structures tend to show as something like the example below.
Front: W"xL" / Back: W"xL" (i.e. 20x15 / 22x15)
If you are asking this, you may be asking to verify what size you are. Please refer to How Do I Measure Myself? If you have additional questions on this please feel free to call us. We are happy to help and will walk you through the process over the phone or in person.