Books like Letters to Penthouse III
Penthouse International
Letters to Penthouse III is 231 pages, about 4 hours 14 minutes at 250 words a minute.
12 books to read next
How long each takes
The Kama Sutra 3.5 h 
The Joy of Sex 4.6 h 
Sex 10.1 h 
The Ethical Slut 5.4 h 
My Secret Life 9.4 h 
Ratirahasya 3.2 h 
Dear G-spot 4.6 h 
The History of Sexuality 3.5 h 
Sex at Dawn 7.3 h 
Understanding Human Sexuality 12.1 h 
Human Sexual Response 6.7 h 
The Ultimate Sex Book 3.5 h Bar height shows length. Estimated at 250 words a minute.