What's a good practical size for a DIY camera jib?

I'm thinking about building a jib crane/boom for my DSLR camera. I've looked at a lot of DIY examples on youtube and have come up with my own design that's a combination of what I've seen from others. My only question now is how long should it be?

I think with my design I can build something safe and sturdy out to about 16' to 18' in length. but is this overkill? I know I've seen good results with DIY jibs half that size, and they always look much larger in-camera. Practically, how large is the "average" jib/crane shot used in Hollywood productions?

Obviously, I want to go as large as I can. But I don't want it so big that it's a real pain to haul around and set up.

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Matt Crunk
Fiveacre Films Inc.
Film and HD Video Production & Post Services