Well it depends on what it is made of. But generally about 3 times that is the norm. 3/4" mdf/medite is the preference of this forum. You can use a jigsaw inside, i do it all the time. You can pick one up from wally world for 25 bucks, or meijer for 20, and a handy panel of 3/4" mdf for around 8 bucks and you can make 10 of your own custom sturdy acceptable baffles. Do it right the first time and you will save money in the long run. Get some non hardening modelling clay from your local craft store, it will say "never hardens" on it. And pick up some edead v1 sound deadener. It is only 1 buck a square foot. 30 bucks should do your doors.