I believe most dualie kites would list a tip to tip measurement in inches as the size. Back when I bought my first sport kite, in the eighties, I had to choose full sail, 3/4 sail or 1/2 sail. The full sail was the then standard 96" tip to tip. At least that is the way Premier was doing it the day I went into Kitty Hawk Kites on the Outer Banks of North Carolina. I knew nothing other than what my budget would allow. Wanted the full sail but my funds would only allow the 3/4 sail, 72" tip to tip. Inquired about line sets & found the price so high that I left the store just happy to get only the kite for eighty bucks plus the govenor's tax. Went back the next day & bought a 150', 200# Skybond line set with a winder & Skyclaw handles. Borrowed that money from my wife. Then we went out in a steady 25 mph wind & did some scudding on the beach. What a day that was....
Too bad I did not keep flying all those years since, SHBKF
Premier Aerosport 3/4 sail, still flyable even