Sourdough Hydration Calculator with Starter Accounting

Start with the ingredients you actually add

Enter the flour, water and starter you weigh into the mixing bowl. Added flour excludes the flour already in your starter; added water excludes its water. Enter the starter's full weight separately. Counting its flour or water in both places would count those ingredients twice.

Simple mode assumes a starter at 100% hydration: equal flour and water by weight. It calculates hydration and current dough weight without salt or scaling. Use Advanced mode when your starter has a different hydration, when you want salt included in dough weight, or when you want to resize an existing recipe.

The two presets are arithmetic examples. They are starting values for understanding the controls, rather than recommendations for flour choice, fermentation or baking. After changing an ingredient, the preset becomes Custom. You can reset to the baseline without changing your selected mode or mass units.

What dough hydration measures

Hydration expresses water mass relative to flour mass. Flour is the denominator:

Here, $H$ is hydration in percent, $W_{\mathrm{total}}$ is all the water in the dough, and $F_{\mathrm{total}}$ is all its flour. Both totals include the starter's contributions. This follows the definition explained in King Arthur Baking's guide to bread hydration.

Salt contributes to dough weight but is neither flour nor water. Adding salt therefore changes the dough's mass without changing this hydration calculation. A hydration above 100% means water weighs more than flour; the calculator does not force every recipe below that value.

The diagram uses a different denominator: total dough mass. It shows how much of the current dough is flour, water or salt after the starter has been split into its components. Its water share is not the hydration result. Use the labeled hydration metric when comparing water to flour.

Split the starter before calculating the totals

For starter weight $S$ and starter hydration $h$ in percent, its flour contribution is:

Add $F_s$ to the separately added flour and $W_s$ to the separately added water. The calculation assumes the starter consists of flour and pure water. It does not estimate moisture contributions from milk, eggs, fruit or other additions.

For example, weigh 500 g flour, 350 g water and 100 g starter at 100% hydration. The starter contributes 50 g flour and 50 g water. Total flour is 550 g; total water is 400 g. The result is:

Current dough weight is 950 g before salt. Dividing just the separately added water by separately added flour would give 70%, leaving out the starter's effect.

A starter does not always raise hydration. Keep the same three weights but set starter hydration to 50% in Advanced mode. It contributes about 66.67 g flour and 33.33 g water. The combined ratio becomes approximately 67.65%, below the added-ingredient ratio. Including the starter makes the calculation complete; it does not imply a particular direction of change.

Resize a recipe without changing its ratios

In Advanced mode, enter salt if it belongs in your recipe, enable Scale this recipe, then enter a target dough weight. The multiplier is:

Here $F$, $W$, $S$ and $A$ are the separately added flour, water, starter and salt masses. Multiply each of those ingredients by the same factor $k$. Because total flour and total water change by that same factor, hydration stays unchanged.

Add 10 g salt to the liquid-starter example above. Current dough weight becomes 960 g. To make 1,200 g of unbaked dough, multiply the recipe by 1.25:

These ingredients total 1,200 g and retain the original 72.73% hydration. The current dough weight card still describes the original recipe; recipe dough weight describes the resized one. When scaling is off, the multiplier is one and the recipe weights match your entered ingredients. The inactive target is ignored.

Weigh in grams or mass ounces

Metric uses grams; Imperial uses avoirdupois ounces of mass. These are not fluid ounces. The conversion uses 1 oz = 28.349523125 g, as listed in NIST Handbook 44, Appendix C, PDF page 335.

Switching units converts the same recipe rather than selecting a different regional formula. The calculator retains unrounded values internally. Displayed ingredient weights use tenths of a gram or thousandths of an ounce, so a displayed total may differ slightly from the sum of individually rounded cards. Copy and print use the same displayed labels and units.

Use a scale suited to your batch size. This tool does not convert cups of flour into mass: packing and ingredient differences would require assumptions beyond the entered recipe. A tiny positive result below the displayed resolution is marked as less than that resolution, rather than presented as exactly zero.

Check an unexpected result

First check whether starter flour or water has been entered twice. Then check the starter hydration and selected mass units. Entering an ounce value while grams are selected changes the recipe rather than converting it.

Ingredient weights cannot be negative. Zero added flour is allowed if starter supplies flour, but total flour from both sources must be positive. Empty, nonnumeric, nonfinite or out-of-range active inputs clear the result and any previous recipe. Very small positive recipes may exceed numerical limits when scaled; increase the baseline amount or reduce the requested target.

Advanced adjustments are ignored in Simple mode. If changing a hidden Advanced value appears to have no effect, switch to Advanced to use it. To start again, use Reset; to keep a record, use Copy or Print. The tool provides no CSV download or saved calculation link.

What this calculation leaves to your recipe

The target is unbaked dough mass, not the weight of a finished loaf. The calculation does not model gas production, evaporation, flour absorption, starter activity or fermentation time. It also does not determine whether a particular hydration will suit your flour or handling method. Use your recipe and observations for those decisions.

Treat scaling as ingredient arithmetic. It preserves the proportions you entered; it does not certify a baking process or guarantee bread quality. Review the ingredient breakdown before weighing a batch, especially when changing starter hydration or moving between units.

References and calculation method

• King Arthur Baking: Hydration in bread dough, explained — definition and inclusion of starter flour and water.
• NIST Handbook 44: General Tables of Units of Measurement — avoirdupois ounce-to-gram relationship.
• OrangeCalc methodology — how calculation assumptions and checks are documented.

The examples above are independently derived from ingredient mass balance. Rounded values are for presentation; the calculation retains full precision until formatting.