The proportions vary greatly.

I have 2 sets of smoking peers, my local people (live within 2 - 3 miles) and people from college (coollege is only 8 miles away but some pepople travel 25 miles in the morning to get there)

The local people consider a "strong" joint as like 30 - 40% weed, yet at college, a weak one is considered about 50% weed. so it varyies massively.

Personally, it depends on why i'm smoking. if it's to relax a bit before a lesson, i'll roll maybe 40 - 55% weed but if im smoking to get raelly stoned i mite go up to like 80% weed.

after reading this thread, im seriously considering rolling a pure weed joint next time i have the afternoon off at college.