Baker's Math for Sourdough: A Beginner's Guide

The Numbers That Add Up to More Than 100%

Baker’s percentages look like a foreign language the first time you encounter them. A sourdough recipe states 100% flour, 75% water, 20% starter, and 2% salt — adding up to 197%. That cannot be right, or so it seems. The system is actually simpler than it appears, and once it clicks, every bread formula on any baking forum or in any professional textbook becomes instantly readable. This guide breaks down baker’s math through a single annotated sourdough formula, compares three bread styles side by side, and provides a troubleshooting reference for the problems that trip up most beginners.

What Baker’s Percentages Actually Mean

In baker’s math, flour is always 100%. Every other ingredient is expressed as a percentage of the flour weight — not of the total dough, and not of the final loaf. This is the one rule that makes the entire system work. If a recipe calls for 1,000 g of flour and 750 g of water, the water is 75% — because 750 is 75% of 1,000. Salt at 20 g would be 2%, because 20 is 2% of 1,000.

The reason percentages total more than 100% is that 100% already accounts for all the flour. Water, salt, starter, and any enrichments are stated on top of that flour baseline. A lean sourdough formula might total 197%, while an enriched brioche could total 189% or higher. Neither figure is wrong — the total simply reflects that baker’s percentage is a ratio system, not a composition breakdown. To compute baker’s ratios from ingredient weights, enter the gram weight of each ingredient and the calculator handles the division.

An Annotated Sourdough Formula

Consider a straightforward sourdough recipe that produces a single large loaf or two smaller boules. The formula below uses round numbers to make the arithmetic transparent.

The total dough weight is 1,970 g. The total baker’s percentage is 197%. Both numbers are correct and expected. The value of this notation becomes apparent when comparing recipes or scaling to a different batch size: set a new flour weight, multiply each percentage by that weight, and every ingredient amount follows.

Suppose you want a smaller loaf using 500 g of flour instead of 1,000 g. Water becomes 500 × 0.75 = 375 g. Starter becomes 500 × 0.20 = 100 g. Salt becomes 500 × 0.02 = 10 g. The ratios are preserved perfectly, and the bread behaves identically to the larger batch. The sourdough quantity calculator for any loaf size automates this scaling for any target weight.

The Starter Math Wrinkle

Here is where sourdough formulas diverge from commercial yeast recipes and where many beginners get confused. A sourdough starter is not a single ingredient — it is a mixture of flour and water. A starter maintained at 100% hydration (equal weights flour and water) means that the 200 g of starter in the formula above actually contributes 100 g of flour and 100 g of water.

This matters for calculating true hydration. The “apparent” hydration from the formula table is 75%, but the real hydration accounts for the flour and water hiding inside the starter.

Breaking down the true totals:

• Total flour: 1,000 g (main mix) + 100 g (from starter) = 1,100 g
• Total water: 750 g (main mix) + 100 g (from starter) = 850 g
• True hydration: 850 ÷ 1,100 × 100 = 77.3%

The difference between 75% apparent hydration and 77.3% true hydration is meaningful. Those 2.3 percentage points affect how the dough handles during shaping, how quickly it ferments, and how open the final crumb structure will be. Professional bakers always use true hydration when communicating formulas. If a recipe from a book or website does not specify whether the starter’s flour and water are factored in, the hydration number is ambiguous — and that ambiguity is a common source of unexpectedly sticky or stiff doughs.

Starters maintained at ratios other than 1:1 (100% hydration) require adjusted arithmetic. A stiff starter at 60% hydration, for example, contributes more flour than water per gram. A liquid starter at 125% hydration contributes more water than flour. The principle remains the same: decompose the starter into its flour and water fractions before calculating true hydration.

Hydration by Bread Style: What the Numbers Feel Like

Hydration percentage is the single variable that most determines how a dough handles and what the finished bread looks and tastes like. The comparison below covers three styles commonly made with sourdough, describing what each hydration level means in practical terms.

The jump from 65% to 78% hydration does not sound dramatic in numerical terms, but the dough behavior changes fundamentally. A 65% dough can be kneaded on an unfloured surface with minimal sticking. A 78% dough will grab onto hands and countertops, requiring stretch-and-fold techniques rather than traditional kneading. At 85% and above, the dough barely holds a shape outside of a container and relies entirely on baking vessel support (a Dutch oven, a sheet pan) for structure. These same hydration principles apply to pizza dough as well — a Neapolitan-style pizza at 60–65% hydration handles very differently from a Roman-style pizza at 75–80%.

Troubleshooting Sourdough by the Numbers

When a sourdough loaf does not turn out as expected, baker’s percentages provide a diagnostic framework. Rather than guessing, express the recipe in percentages and compare against the target values for the bread style. The table below maps common symptoms to their likely causes and fixes.

The common thread in these fixes is precision: knowing the actual hydration, the actual fermentation time, and the actual temperature. Baker’s percentages provide the precision for ingredients; a kitchen thermometer and a timer handle the rest. Understanding why weighing flour matters for bread baking reinforces this principle — a cup of bread flour can vary by 30 g or more depending on scooping technique, and in sourdough that variance translates directly into hydration error.

Starter Feeding Ratios and Their Effect on Bread

The feeding ratio of a sourdough starter — the proportion of old starter to fresh flour and water — directly affects how the starter behaves, which in turn affects the bread. Common feeding ratios are expressed as starter : flour : water by weight.

• 1:1:1 (equal parts): Peaks in 4–6 hours at 24°C. Produces moderate sourness. Good for bakers who bake daily or every other day.
• 1:3:3 (low inoculation): Peaks in 8–12 hours at 24°C. Produces a milder, more complex flavor with less acetic acid. Suited to overnight feeding schedules.
• 1:5:5 (very low inoculation): Peaks in 12–18 hours at 24°C. Produces the mildest sourness and the most yeast-driven rise. Used by bakers who want minimal tang.

The feeding ratio also determines how much starter to maintain. A 1:5:5 ratio with 10 g of old starter requires 50 g of flour and 50 g of water per feeding — producing 110 g of starter at its peak. Planning backwards from how much starter the recipe needs avoids the common beginner mistake of maintaining too little starter and having to do multiple feedings before a bake.

Temperature interacts with feeding ratio. A 1:1:1 feeding at 30°C may peak in just 3 hours, while the same ratio at 18°C could take 10 hours. In warm kitchens during summer, a higher ratio (1:3:3 or 1:5:5) prevents the starter from exhausting its food before you are ready to mix the dough. In cold kitchens during winter, a lower ratio (1:1:1) ensures the starter reaches peak activity within a manageable timeframe. To convert between yeast types and sourdough starter, the yeast conversion tool provides equivalent amounts when adapting a commercial yeast recipe for natural leavening.

A First Loaf: Where to Start

For a first sourdough bake, a conservative formula reduces the number of variables that can go wrong. The target: a country-style loaf at 70% true hydration using bread flour, 20% starter (at 100% hydration), and 2% salt.

Here is how to set up the formula for a single loaf.

1. Choose the flour weight: 500 g of bread flour (12–13% protein) produces a loaf of about 750 g before baking — a good size for a first attempt.
2. Calculate the starter amount: 500 g × 20% = 100 g of starter. This contributes 50 g flour and 50 g water (at 100% hydration).
3. Calculate true flour total: 500 g + 50 g = 550 g.
4. Calculate water for 70% true hydration: 550 g × 70% = 385 g total water. Subtract the 50 g from the starter: 385 g – 50 g = 335 g water in the main mix.
5. Calculate salt: 550 g × 2% = 11 g.

The final recipe: 500 g bread flour, 335 g water, 100 g starter, 11 g salt. Total dough weight: 946 g. This 70% hydration is forgiving enough to shape without advanced technique, produces a pleasant open crumb, and ferments predictably at room temperature in 4–6 hours during bulk fermentation. From this baseline, adjustments become straightforward: increase water by 25 g (roughly 5% hydration) for a more open crumb, or reduce by 25 g for easier handling.

The deliberate choice of 70% — rather than the 75–78% seen in many online recipes — gives a new baker room to learn shaping and timing without fighting a highly extensible dough. Handling confidence matters more than crumb aesthetics for the first several bakes.

Where the Calculators Help

Baker’s math removes guesswork from sourdough, but the arithmetic can be tedious when adjusting for different starter hydrations, multi-flour blends, or varying batch sizes. The baker’s percentage calculator handles the conversion between weights and percentages in both directions, while the sourdough quantity calculator factors in starter hydration and pre-fermented flour automatically.

For bakers still transitioning from volume-based recipes, the volume-to-weight conversion for flour types provides ingredient-specific gram weights — a necessary first step before any percentage calculation can be accurate. And once the fundamental ratios make sense for bread, the same logic extends to every flour-based formula in the kitchen.

The numbers in baker’s math are not abstract. Each percentage point of hydration corresponds to a tangible difference in dough feel. Each percentage point of starter determines how long fermentation takes. Each percentage point of salt governs both flavor and fermentation speed. Learning to read these numbers — and to adjust them deliberately — transforms sourdough from a mysterious art into a repeatable process. The mystery is not gone; it just moves from the formula to the fermentation, where it belongs.