Sorry for the late feed back...not sure the length size had the necklace for years, loved it, but never put it on and thought someone eles can get more use out of it then the years it spent in my jewelry box. :)
Please tell me why you can't put your chain against a tape measure or a simple ruler to see how many inches long it is. The common lengths are 16, 18, 20 or 22 inches. If you have an 8 x 11" piece of paper and the chain when placed next to the 8" side can cover the 8" distance two times, the the chain is 16" ( 2 x 8 = 16) Do you just not want to measure it or are you unable?