Baker's percentage — or baker's math — is the system professional bakers use to write and scale recipes. Once it clicks, “75% hydration sourdough” stops being jargon and becomes something you can read at a glance. The whole system rests on one rule and one formula.
The one rule: flour is always 100%
In baker's math, the total flour in a recipe is always defined as 100%, and every other ingredient is expressed as a percentage of that flour weight — not of the whole recipe. If you use two flours, their weights add together to make the 100%.
The formula
That's it — the same formula works for water, salt, yeast, butter, sugar, everything. Each ingredient is calculated independently against the flour.
A worked example
Take a simple sourdough: 1000 g flour, 700 g water, 20 g salt, 200 g starter. Flour is 100%. For each other ingredient, divide by the flour weight:
So you'd describe this loaf as “70% hydration, 2% salt, 20% starter.” Another baker anywhere in the world can read that and reproduce it at any size.
Why the percentages add up to more than 100%
This is the part that confuses everyone at first. In normal percentages, the parts add up to 100%. In baker's math they don't — because every ingredient is measured against flour, not against the total. Our example sums to 100 + 70 + 2 + 20 = 192%, and that's correct. A total over 100% is normal and expected.
Scaling a recipe with baker's percentage
Because every ingredient is pegged to flour, scaling is trivial: pick a new flour weight and multiply each percentage by it. Want a bigger loaf? Set flour to 1200 g and recompute — water becomes 1200 × 0.70 = 840 g, salt 1200 × 0.02 = 24 g, and so on. The dough behaves identically because the proportions never changed.
Sources and method: see our methodology and references.