Baker's Percentage, Explained

Baker’s percentage is a way of writing a recipe where every ingredient is expressed relative to a defined flour weight, which is always 100%. The important detail for sourdough is whether that baseline includes the flour already in your starter. State the convention before comparing two recipes. King Arthur’s baker’s-percentage reference explains flour as the baseline for a formula.

The one rule

Flour is the baseline. Everything else is measured against it:

ingredient % = (ingredient weight ÷ total flour weight) × 100

In this guide, total flour includes the flour inside the starter, and total water includes its water. This matches our hydration guide and calculator. Percentages can add up to more than 100% because flour, rather than the whole dough, is the baseline.

Some recipes instead quote water and starter relative to the flour added at mixing. That is a useful mixing instruction, but its water percentage is not the finished dough’s total hydration.

Scaling a formula

For 800 g total flour, 75% total hydration, and 2% salt, the total formula is:

Ingredient	Total weight	Baker’s percentage
Flour, including starter flour	800 g	100%
Water, including starter water	600 g	75%
Salt	16 g	2%

Assume you use 160 g of starter at 100% hydration. That starter supplies 80 g flour and 80 g water. Subtract both contributions before mixing:

• Add 720 g flour: 800 − 80.
• Add 520 g water: 600 − 80.
• Add 160 g starter and 16 g salt.

The starter weighs 20% of total flour, but only 10% of the total flour is prefermented. Do not count the starter a second time after including its flour and water in the totals.

By comparison, 800 g added flour + 600 g added water + 160 g of the same starter contains 880 g total flour and 680 g total water: 77.3% total hydration, not 75%.

To scale the worked formula, multiply all four mixing weights by the same factor. Doubling gives 1,440 g added flour, 1,040 g added water, 320 g starter, and 32 g salt. Mixing and fermentation timing may still need adjustment for the larger batch.

Why it’s worth learning

• Repeatability — the same percentages preserve ingredient proportions at any size.
• Comparison — you can line up two recipes and see, at a glance, that one is wetter or saltier than the other.
• Troubleshooting — when a bake goes sideways, percentages tell you which lever to pull.

Baker’s percentage pairs directly with dough hydration — hydration is simply the water percentage. If you’d rather not run the arithmetic by hand each time, Sourdough Journal keeps baker’s percentage, hydration, scaling, and levain calculations tied to the formula you’re actually baking, and saves the result alongside your starter and bake notes.