Hulda Clark 's book, or somewhere on the net quoting her, will probably tell you how much coQ10 to use.
By the way many products sold at Health Food stores & elsewhere actually cause coQ10 to be depleted. This happened to me as I found out thru testing - I had practically none & took a tablet every day.
If you are over say 35 you need it in the form of ubiquinol. I get mine at wholehealth.com. No soy for one thing.