Hi Bull, actually I don't recommend you to make a 100% accurate math on how much juice is lost, what you have to maintain clear is that this will make you lose value.
So, if you really need to make those redirects, try to reduce them to only one step, but, for ease of management if you REALLY need to create two steps redirects consider that you'll be losing the same value you'll be losing from one page linking to another and to other one (further reading here).
For page rank (juice) purposes 301 are treathed as links. However what I recommend you is after having put in place the generic redirect rules, identify your best traffic delivering pages and create an ad-hoc 301 for those ones, so you'll be sure those urls will receive least impact in that sense.