Baker's percentage is the system professional bakers use to write and scale recipes. Once you understand it, you can adjust any bread recipe perfectly and diagnose exactly why a loaf went wrong.
Every professional bakery recipe is written in baker's percentages. It looks confusing at first — percentages that don't add up to 100 — but once you understand the logic, it's the most useful system in baking.
In baker's percentage, flour always equals 100%. Every other ingredient is expressed as a percentage of the total flour weight.
This is why the percentages in a recipe don't add to 100 — they're not slices of a pie, they're ratios relative to flour. A recipe with 100% flour, 65% water, 2% salt, and 1% yeast has a total of 168%, which is perfectly normal.
A standard recipe says "500g flour, 325g water." That's useful for making one batch. A baker's percentage recipe says "65% hydration." That's useful for:
The water percentage — called hydration — is the single most important number in bread baking. It determines how the dough handles, how the crumb opens, and how the crust forms.
Suppose you want to make a loaf using 750g of flour instead of 500g. You don't need to recalculate the whole recipe — just multiply each percentage by your new flour weight divided by 100:
When using a sourdough starter, the calculation gets slightly more involved because the starter itself contains both flour and water. A 100% hydration starter is equal parts flour and water by weight — so if you use 200g of starter, you're adding 100g of flour and 100g of water to your recipe. To maintain your target dough hydration, you need to account for this and adjust your added flour and water accordingly.
This is also why sourdough recipes often specify the starter hydration explicitly — a 100% hydration starter behaves very differently from an 80% one.