Baker’s Percentage: A Clear Guide for Sourdough

Flour is the reference point

Baker’s percentage describes an ingredient’s weight compared with the total flour in a dough. Flour is always 100%. Water, salt, and every other ingredient are measured against that same flour weight, not against the weight of the finished mixture. Once that reference point is clear, a formula becomes easier to compare, resize, and check before mixing.

The basic calculation is ingredient percentage = ingredient weight ÷ total flour weight × 100. If a dough contains 600 g flour and 12 g salt, its salt percentage is 2%. This does not mean that 2% of the dough is salt. It means the salt weighs two hundredths as much as the flour. King Arthur Baking’s professional reference documents this convention; the numerical examples in this guide are independent worked calculations.

Why the percentages exceed 100

Consider a simple formula with flour at 100%, water at 72%, and salt at 2%. Its percentages add to 174%. Nothing is wrong: these are flour-based ratios, not slices of a pie representing the whole dough. Each ingredient has its own relationship to a fixed reference weight.

With 600 g total flour, multiply 600 by 0.72 to find 432 g water, and by 0.02 to find 12 g salt. The dough weighs 1,044 g before handling losses. Dividing that total by the flour weight gives 1.74, the same relationship represented by 174%. Keep the distinction between a percentage and its decimal form visible: 72% becomes 0.72 in multiplication, while 174% becomes 1.74.

Sourdough starter contains flour and water

Starter is an ingredient you weigh, but it is also a mixture. Its flour and water belong in the formula totals. A 100% hydration starter contains equal flour and water weights. Therefore, 120 g of that starter contributes 60 g flour and 60 g water. Its bubbles do not change how this bookkeeping convention is applied.

To make the 600 g flour, 72% hydration example with that starter, weigh 540 g fresh flour, 372 g fresh water, 120 g starter, and 12 g salt. These mixing weights still total 1,044 g. The flour calculation is 540 + 60 = 600; the water calculation is 372 + 60 = 432. Leaving starter flour out of the denominator would describe a different ratio and obscure what is actually in the dough.

Keep a formula separate from a mixing list

A total formula describes the dough’s composition. A mixing list tells you what to put in the bowl. Both are useful, but they answer different questions. The total formula above contains 600 g flour, 432 g water, and 12 g salt. Its mixing list contains fresh flour, fresh water, starter, and salt, because part of the flour and water has already been combined and fermented.

Do not add 120 g starter on top of the total formula without subtracting its flour and water. That would produce 660 g total flour and 492 g total water, making a larger dough at approximately 74.55% hydration. It would also lower the actual salt percentage to about 1.82%. A small-looking accounting shortcut therefore changes several characteristics together.

Two different meanings of starter percentage

A formula may say 20% starter and mean starter mass divided by total flour. Our example uses 120 ÷ 600 × 100 = 20% starter mass. Prefermented flour percentage counts only the flour carried in that starter: 60 ÷ 600 × 100 = 10%. These numbers describe the same dough from different perspectives.

At 100% starter hydration, starter mass percentage is twice prefermented flour percentage. At other starter hydrations, that shortcut fails. A 60% hydration starter containing 60 g flour weighs 96 g because it contains 36 g water. In the same 600 g flour formula, it represents 10% prefermented flour but 16% starter mass. Always read the label beside the number instead of assuming every recipe uses the same convention.

Splitting a starter at any hydration

Write starter hydration as a decimal h. Starter flour = starter mass ÷ (1 + h). Starter water = starter mass − starter flour. For a 90 g starter at 80% hydration, h is 0.8, so starter flour is 90 ÷ 1.8 = 50 g and starter water is 40 g. This is simple mixture arithmetic, not a prediction about starter maturity.

If the starter’s hydration is unknown, an exact overall hydration cannot be recovered from its weight alone. A thick appearance is not enough to establish its composition because flour type and fermentation affect texture. Use a known feeding record, rebuild a measured portion with a documented formula, or label the result as an estimate. Extra calculator digits cannot repair missing ingredient information.

Combining different flours

When several flours are present, their percentages share the same denominator and must add to 100%. A 600 g flour formula could contain 540 g bread flour and 60 g whole wheat flour, corresponding to 90% and 10%. The flour inside the starter also belongs to one of those categories, or to a documented blend.

If our 120 g starter contains 60 g bread flour, the fresh flour list becomes 480 g bread flour plus 60 g whole wheat flour. If instead its flour is entirely whole wheat, the fresh flour list becomes 540 g bread flour with no additional whole wheat. Both versions have the same total flour proportions, but they distribute the fermented flour differently. That distribution is useful information to preserve in a recipe note.

For a blended starter, split its flour before subtracting anything from the final mix. Suppose the 600 g total flour target is 80% bread flour and 20% rye, and the starter’s 60 g flour is a 60:40 bread-to-rye blend. The starter supplies 36 g bread flour and 24 g rye. Fresh additions are therefore 480 − 36 = 444 g bread flour and 120 − 24 = 96 g rye. Check that 444 + 96 + 60 = 600 g. A blend label describes the flour, not the whole starter.

Working from percentages back to grams

Choose total flour first when flour supply is the constraint. For 800 g total flour at 72% hydration and 2% salt, the totals are 576 g water and 16 g salt. At 10% prefermented flour, reserve 80 g of the flour for the starter. With a 100% hydration starter, that means 160 g starter containing 80 g water.

The final mixing list is therefore 720 g fresh flour, 496 g fresh water, 160 g starter, and 16 g salt. Add the weights to get 1,392 g dough. Then reverse the calculations as a check: water is 496 + 80 = 576 g, flour is 720 + 80 = 800 g, and 576 ÷ 800 is 72%. Checking in both directions catches accidental double counting.

Working backward from dough weight

If the dough size is the constraint, divide the target weight by the sum of the decimal formula ratios. A flour-water-salt dough at 72% hydration and 2% salt has a multiplier of 1 + 0.72 + 0.02 = 1.74. To make 1,740 g dough, calculate 1,740 ÷ 1.74 = 1,000 g total flour.

That produces 720 g total water and 20 g salt. With 10% prefermented flour at 100% starter hydration, use 200 g starter, 900 g fresh flour, and 620 g fresh water. Starter is already represented within the flour and water totals, so it must not be included again as an extra 20% in the dough multiplier. This method estimates mixed dough weight, not the lighter weight of the cooled baked bread.

Adding ingredients without hiding assumptions

Oil, seeds, sugar, and other additions can also be expressed against total flour. For example, 24 g oil in a 600 g flour dough is 4%. If it is an additional ingredient, add its weight to the dough total. It does not become water merely because it pours. A soaker needs more careful records: distinguish its dry ingredients from its water, and note whether unabsorbed water is drained.

Milk, eggs, yogurt, honey, and cooked grains complicate a hydration calculation because their full weights are not pure water. A basic flour-water calculator should state what it includes instead of presenting a misleadingly precise answer. For an enriched dough, keep the original recipe’s convention visible and use ingredient composition data only when you deliberately want an estimated water-content calculation.

Rounding and measurement

Carry extra precision through the calculation and round the final mixing list to suit the scale. If each intermediate result is rounded separately, small errors can accumulate, especially in a tiny batch. For a normal home-sized dough, recording major ingredients in grams is a practical starting point, while small salt quantities may benefit from a more sensitive scale.

After rounding, add the final weights and recalculate the actual percentages if the differences matter to your comparison. A printed target of 72% might become 71.96% after rounding; that is a measurement detail, not a different baking philosophy. More significant discrepancies often reveal the wrong flour denominator, a starter counted twice, or a quantity entered in the wrong unit.

Reading the numbers without overpromising

Baker’s percentages make composition comparable, but they do not make every dough behave identically. Two formulas at the same hydration can use different flours, different starter maturity, and different mixing and fermentation methods. The numbers are a map of ingredients, not a substitute for observing the dough or following a sound method.

Use the formula to answer concrete questions: how much water is present, how much flour was prefermented, how much salt is included, and what batch size will result. Then record the process separately. A useful note includes the flour identity, starter feeding record, ingredient weights, temperature observations, and any changes actually made. That turns a calculator result into a recipe you can understand and revisit.

A final five-question audit

Before weighing ingredients, ask whether all flour is included, whether the starter hydration is known, whether starter percentage means mass or prefermented flour, whether water added later has been counted, and whether the total dough weight matches your intended portions. These questions are more useful than memorizing a large collection of isolated percentages.

For the recurring example, the answers are 600 g total flour, 100% starter hydration, 20% starter mass or 10% prefermented flour, 432 g total water, and 1,044 g mixed dough. Once you can trace those five values through the ingredient list, you have the essential skill. Larger batches and different hydrations use the same relationships, with a different set of numbers.