I'm not a professional baker but i have been successfully baking as an amateur for a couple of years now. In this time I have learned a few basics, such as that strong white flour can absorb water of 60% of the flour weight (approximately). That is, 3/8 water to 5/8 flour. I know that this is flour dependent, but only within a couple of percent.
Just found a gem of a tip:
"The more protein a flour contains, the more water it absorbs. Flours can vary more than 20% in their ability to absorb moisture."
Meaning.... when substituting flours in a recipe, you will need more or less water (moisture) if you use a flour with a different protein content!