Hydration is water as a percentage of flour weight, and everything in a bread formula follows the flour. A dough with 500 grams of flour and 350 grams of water is 70 percent hydration. Salt is usually 2 percent of flour, levain 15 to 25 percent.
To convert a recipe, pick the flour weight, then multiply. For 750 grams of flour at 75 percent hydration you need 562 grams of water, 15 grams of salt, and a levain of roughly 150 grams. Keep the starter's own flour and water in mind only when scaling precisely.
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Higher hydration is not automatically better; it extends fermentation speed and makes shaping harder. Move up in steps of five points, not twenty, and note what changes.