Here’s the simple mathematical formula for solving this problem:
1. Divide the word count of the book by your rate of speech per hour to get the number of finished hours. If you don’t know your rate of speech, Audible uses 9400 words per hour, or 157 words per minute, in its calculation for books posted on ACX.
2. Multiply the number of finished hours by 6. This number is a very conservative estimate of the number of real-time hours you will spend in preparing to read (pre-reading the book, looking up pronunciations, etc.), recording, editing, and transmitting your book. For instance, a 10-hour book may require 60 hours of your life from the time you read the first word until the last byte is uploaded or mailed to the client.
3. Multiply the real-time hours by the hourly rate of pay you need to survive. Chances are very good that you will come up with a pay rate for this audiobook that is $1000s MORE than your client wishes to pay. You have to decide how to negotiate a rate acceptable to both of you.