The 'traditional' length of a fiction novel is 60k words. Although I believe 90k is a more common expected length today (looking at publisher submission require

The 'traditional' length of a fiction novel is 60k words. Although I believe 90k is a more common expected length today (looking at publisher submission requirements). Obviously non-fiction is much more variable, both in length and time required to read. E.g.: it's going to be significantly more time consuming to read a physics text that walks you through (even rudimentary equations) than a step by step illustrated guide to photography.