There is no common measurement for how much yardage is in a ball or skein of yarn.
You'll need a little over five to get the necessary yardage, so buy six and you should be fine.
If I had a pattern for a scarf similar to the length I was looking for and around the same gauge as the yarn I was looking at, I might assume that the yardage requirements would be similar.
We played some really good rugby with the forward dominating the scrum and making excellent yardage with ball in hand.
Penguin or Pingu launch the rules are simple you simply batter the poor defenseless creature with a club and attempt to gain maximum yardage.