Core idea
Total flour is always 100%.
Every other ingredient is measured as a percentage of total flour weight.
This lets a formula scale from one loaf to many loaves without changing the ratio.
Example
If flour is 500g and water is 375g, hydration is 75%.
If salt is 10g, salt is 2%.
Related calculators
DoughMath guides are educational explanations for formula math. Use the linked calculators for exact weights before baking.