Sourdough hydration calculator
A hundred grams of 100% hydration starter is fifty grams of flour and fifty of water. Most hydration calculators ignore this, so a dough built on 500 g of flour with 20% starter really holds 550 g of flour, and 75% hydration means 413 g of water rather than 375. Pour the 375 on top of the starter instead and the dough lands nearer 77%. At low starter percentages the difference is small; at 30% or more it is enough to change how the dough handles.
Baker's percentages state every ingredient against the total flour weight, and a starter is part of that flour. Weigh 500 g of flour with 20% starter at 100% hydration and the dough holds 550 g of flour, so 75% hydration is 413 g of water — the starter already brings 50 g of it, leaving 363 g to pour in.
How to build a sourdough
Hydration is the main lever on both handling and crumb. Below about 65% the dough is stiff and the crumb tight; around 75% it is workable and open; past 80% it becomes slack, needs coil folds rather than kneading, and rewards a banneton and a hot Dutch oven. None of these are better or worse: a bagel wants 55% and a ciabatta wants 85, but the number tells you what technique the dough will demand before you start.
Questions
Every ingredient stated as a percentage of the flour weight. Flour is always 100%.
70–75% for a first sourdough, 80%+ once you can handle a slack dough. Bagels sit near 55%.
It should. A 100% hydration starter is half flour and half water, and both belong in the totals.
Two per cent of flour weight is standard. Below 1.5% the dough slackens and the flavour flattens.
Ten to twenty per cent for a slow overnight rise, thirty or more for a faster one. Less starter means more time and usually more flavour.