How did you come up with your goal weight?....

Figured out approximately how much fat I had in my body, figured out how much weight I'd need to lose to get my bodyfat% down to a lean(but healthy) level.
That became my goal weight (for now).

Ultimately I plan on gaining much of this weight back, but while maintaining a lean(ish) bodyfat %.
Initial cut, then slow & gradual bulk, then maybe cut a couple kg at the end, then maintain. Such is the plan right now anyway

I picked the lowest weight I remember weighing back in high school, 140 lbs. It's towards the upper end of the healthy BMI range for my height.

However, at the rate I'm shedding sizes I may need to evaluate a little sooner than that. I'm only 5'4", 218.6 lbs as of this morning, and only about 5 lbs out of size 14, so I think I must have a fair bit more muscle mass than I thought I did. The whole way along, I'm going to be seeing how I look in the mirror and how fit I feel. If I'm in a size 8 or 10 at 160 lbs and feel fantastic, I'll stop there. If I get to 140 lbs and I'm still flabby, I'll probably switch to working on lowering body fat instead of losing lbs.

For me the plan is to be at the top-end of the 'normal' BMI range. Though I would settle for a few pounds more than that, since I do have quite a large frame, and am never going to be (or want to be) skinny.

I've just guessed at 4 stones down - but my goal weight is whatever I am happy with, when I'm happy with my clothing on me and when I am happy inside. Don't know what number that will be. But as an estimate I'm guessing at a UK size 14 ish.

Clothing sizes don't really mean much. I am currently wearing sizes 10, 12, 14, and 16, none of which is too large or too tight. For most purposes, I would consider myself to be in the lower half of the 14 range.
Actually, I should say, "for most clothing in the price range I buy, I am in the lower half of the 14 range."

My original goal weight was the weight I was at my wedding, I was very happy with it. (ps, hit my original goal weight this weekend!). However, I still have a lot of fluff. My coworker is the same heights me with a rocking body. So my new goal weight is where she is around her weight. May adjust when I get there though.

I picked the low end of the healthy BMI range for my height, so that I'd have a little wiggle room without running the risk of heading back into the overweight range. I've also visited sites like Model Mayhem and My Body Gallery, where I plug in my height and my goal weight (and bra size on Model Mayhem) and the majority of the people with those numbers look "just right" to me.

Obviously, that's all speculative superficial stuff and the weight I decide to start maintaining at will ultimately be just whatever I feel healthiest at, of course.