I take a somewhat different approach. I know my height and I have an estimate of the body fat percentage I'd like to have and the approximate lean (nonfat) mass I'd like to have. Then I reverse engineer the resulting weight:
height - 155cm (61")
LBM - 43-45kg (95-99#)
fat % - 12-15% (==> 85-88% lean)
45/.88 = ~51kg (112.5#) <---- target weight
Though I don't really care much about weight. I care about health, and capability, and performance. Weight is something easy to measure, so we look at it like the drunk looking for his car keys under the streetlight.
I'm leaning toward going for BF% myself, because even with a large range, most calculators are just guesses based on some formulation of 'average'.
I'm 6'3", athletic build, and my supposed healthy range is 148 (yeah right) - 200. I could reasonably see myself at ~195, but I'm not convinced that my best weight is under 200. I've got broad shoulders, long arms, full back/chest, all naturally. Weight is reasonable to monitor, but ultimately not the best indicator of health.
I think estimating a natural ideal body weight is harder for men, because they naturally have a wider range in the amount of muscle they can develop and maintain without any extraordinary effort. My DH is 5'11" and also has very broad shoulders and long limbs. His "healthy weight" range is something like 135-175. Because it had been so long since he was under 200, he wasn't sure where his final stopping point would be. At 175 he looked quite slender with clothes on, but was unhappy with the amount of fat around his middle. Now at 165, and with a modest commitment to regular body weight exercise, his upper body is noticeably more muscular and his waist is 2" smaller. He looks downright skinny in clothes (by American standards anyway), but he is very happy with the definition starting to appear in his abs.
I'd guesstimate his body fat % to be in the high teens. He probably could easily put on 10lbs in muscle and still look slender. He has the skeleton to support that and more. However, he's almost certainly a hard gainer. The amount of work, in terms of weight lifting, to make sure that 10lbs was muscle and not fat is not something that interests him at the moment. So even though he could support a weight above his calculated "healthy weight", he's decided to settle for looking skinny right now. He looks damn good naked tho.:cool: