This keeps people awake at night but I now have the answer.
How long is a roll of toilet paper? Five a month!
OK, so I bought some toilet paper and it wasn't the "right kind" so I had to use it in my back toilet and get my wife her favourite brand for the en-suite.
Trouble is I'd got the biggest packet and the 36 rolls lasted just over 7 months hence "Five a month!".
You can all rest easy now.
More fun later,
FunFromOz.