I've had a really hard time with this topic as well. I did a lot of searching and found an answer that made sense to me. I’m not sure if this is accurate, but it’s what I go by:
"A nutritionist friend of mine advised me years ago that for a paste type marinade (eg pesto) assume 1 tbsp of the marinade sticks to each 85 grams (3 oz) meat.
For a oil based liquid marinade, assume 0.5 tbsp of the marinade sticks to each 85 grams (3 oz) meat.
For a non-oil liquid based marinade (eg juices or wine etc) assume 1/3 tbsp sticks to each 85 grams (3 oz) of meat."
Source –
CalorieCount.About.com Forums
I hope that's helpful!