Length of a loop for adults

Maybe you can help me out:
if I want to make a loop scarf, how many centimeters in length and width should I plan for an adult? I’m planning to wrap the loop around my neck twice. Wrapping it around the neck three or four times would be too much, right? In that case, would I need to use thinner yarn and also make the loop narrower?

Thanks for all your helpful answers :)

The length of an infinity scarf depends on whether you want to wrap it around your neck just once or twice.
When knitting or crocheting, you should definitely aim for about one meter in length; for multiple wraps, rather well over one meter.
It would be practical if you checked every now and then while knitting or crocheting whether it is already long enough.

I found a pattern for a knitted infinity scarf for you here, even with videos.
There are also lots of helpful tips there.
http://eska-kreativ.blogspot.de/2012/01/grundkurs-stricken-loopschlauchschal.html

That’s a good question—I’ve actually been wondering the same thing.
Welcome, HaseHaseSternchen—I think it’s great that you’re sharing this info.