Hydration refers to the amount of water, relative to the amount of flour, and this must be done by weight. I prefer grams for bread. Of course, any weight measure will work, as long as you are talking weights. Soooo, if you start with 500 grams of flour, then you want 500gms of flour x .70=350 grams of water. Ounces would be similar.
The SS Platypus, sails again, to the support of the Vets!
"perhaps...but then again...maybe not..."