Captain Zappa

I have looked at many sites and forums to find out definitively how to measure a triangle landing net to gauge size ie 36, 42, 50 " etc, all i find are either idiots making stupid comments because they probably haven't got a clue or half answers, many say measure the arms!!, but does that mean measure both arms and add that together or the whole perimeter of the net arms plus string, so please can anyone give me a straight concise answer, thank you