Weight seems to vary with gauge of yarn. For instance, I used to use a now-defunct Rowan Aran-weight that was in 140m long, 100g hanks. On the other hand, they also used to do 25g hanks of much finer gauge, although I can't remember the length.
Slightly off-topic, you've reminded me of a visit to the Cutty Sark - there's a deck with exhibits and displays including one describing how the ship used to bring back wool from the antipodes. According to the display, one sheep's fleece would yield 3000 miles of yarn. Do the maths. If 140m weighs 100g, then 3000 miles, which is 4,828,032 metres, would yield 4,828,032/140 m or 34485 hanks or 3448.6 kg - that's some sheep! I think somebody read 3000m and went imperial rather than metric! I did tell them about four years ago but it was still there the last time we dropped by in autumn 2016.