About the Sourdough Baker’s Math Calculator
This is a full baker’s-percentage workbench, not just a hydration slider. Set total flour to 100% and it computes exact gram weights for water, starter, and salt, then does the thing most calculators skip: it accounts for the flour and water hidden inside your starter so the hydration you asked for is the hydration you actually get. It works forward (design from percentages), in reverse (scale to a starter weight you already have), and across preferments (poolish, biga, and levain splits), and it estimates bulk fermentation time from your dough temperature.
It is built for the sourdough baker leveling up from a fixed recipe to true formula thinking, the baker scaling a loaf up for a crowd or down for a single bâtard, anyone converting a percentage formula from a book into gram weights, and bakers chasing consistency who want the same hydration whether they feed a stiff or a liquid starter.
Everything runs locally in your browser. Your formula, batch size, and saved house recipes never leave your device — the page makes no network call after first load, and saved formulas live in your browser’s local storage.
Two caveats worth internalizing: the bulk-time estimate is a starting guide, not a timer — starter strength, ambient humidity, and flour vary too much to predict to the minute, so judge by a 30–50% rise and a jiggly, airy feel. And hydration is not a score: an 85% open-crumb loaf is not “better” than a 68% sandwich loaf, just different. Pick a hydration that matches your flour strength and the bread you actually want to eat.
Enter the time you want to pull the loaf from the oven and get a back-timed schedule with an overnight cold proof.
Whole grains drink more water. Enter their share of your flour to get an adjusted hydration and the flour split in grams.
How much starter to keep and at what feeding ratio — get the flour and water to add.
Name and store your go-to formulas, then reload them any time.
How to Use the Baker's Math Calculator
Start by choosing a mode. Forward is the everyday choice: enter your total flour weight and set hydration, starter, and salt as percentages to get exact gram weights. Use Reverse when you fed your starter and want to build a loaf around exactly what you have — the tool solves the total flour so your starter lands at your chosen percentage. Use Preferment to split off a poolish, biga, or levain the night before. Whatever mode you pick, the calculator quietly subtracts the flour and water already living in your starter so the hydration number you see is the hydration you actually get.
The 100% Flour Convention
In baker’s percentages, flour is always 100% and every other ingredient is measured against it. Water at 75% means 750 g of water for every 1,000 g of flour; salt at 2% means 20 g. The genius of the system is that it is scale-independent — the same formula describes a single loaf or a hundred, and two bakers an ocean apart can compare recipes without converting cups. Note that percentages can add up past 100%, which confuses newcomers: a 75% hydration, 20% starter, 2% salt dough totals 197% of the flour weight, and that is exactly right.
Hydration, Strength, and Crumb
Hydration is the biggest lever on your crumb. Lower hydration (65–70%) makes a tighter, sandwich-friendly crumb that is easy to shape and forgiving for beginners. Higher hydration (78–85%+) opens the crumb into the dramatic irregular holes of an artisan loaf but demands strong flour and confident handling. The catch is that hydration must match your flour’s protein and your skill: a weak all-purpose flour cannot hold 85% water and will spread into a puddle. Start at 72–75% with good bread flour and climb only once your shaping is reliable.
Why Dough Temperature Beats Clock Time
Fermentation is driven by temperature, not the clock. A dough at 26°C ferments roughly twice as fast as the same dough at 20°C, which is why the same recipe that bulks in 4 hours in summer can take 8 in a cold winter kitchen. This calculator estimates bulk time with a simple rule — it doubles roughly every 6°C drop in dough temperature — but treat it as a guide and read the dough itself. Bulk is done when the dough has risen 30 to 50%, feels airy and jiggly, shows some bubbles at the edges, and holds a gentle dome. Controlling dough temperature (with cooler or warmer water at mix) is the single most reliable path to consistent bread.
Poolish vs Biga vs Levain
Preferments build flavor and strength before the final mix. A poolish is a loose 100% hydration preferment that adds extensibility and a mild, slightly nutty sweetness — classic in baguettes. A biga is a stiff 50–60% hydration Italian preferment that adds strength and a deeper, more complex flavor, favored for ciabatta and focaccia. A levain is simply a sourdough preferment built from mature starter, tuned to the flavor you want by adjusting its hydration and how ripe you let it get. The tool splits your flour and water into the preferment and the final dough automatically for whichever you choose.
Salt: Why 2% Is the Magic Number
Salt at around 2% of flour weight is the near-universal standard, and for good reason. Below about 1.5% bread tastes flat and ferments too fast because salt is missing its brake on yeast and enzyme activity; above about 2.5% it noticeably slows fermentation and tightens the crumb. Salt also strengthens the gluten network and improves crust color. Add it after an autolyse rest rather than directly onto the starter, where its osmotic pull can stress the culture. For most loaves, 2.0% is the safe home for flavor, structure, and fermentation control at once.
Scaling Up: From One Loaf to Twenty
Because the formula is percentage-based, scaling is pure multiplication — but two practical limits appear at volume. Mixing gets harder as batches grow, so high-hydration doughs benefit from a mechanical mixer or a longer series of stretch-and-folds. And fermentation timing shifts because large dough masses hold their own heat, fermenting faster than a single loaf in the same room. When you scale a tested single-loaf formula up for a bake sale or a dinner party, expect to shave a little off the bulk time and keep a closer eye on the dough. This calculator keeps the ratios exact at any batch size so the only variables left to manage are the ones your hands control.
Looking for more kitchen tools? Try the Pizza Dough Calculator for Neapolitan and New York styles, the Recipe Scaler to resize any recipe, or browse all Cooking & Kitchen tools.
Frequently Asked Questions
Why is everything expressed as a percentage of flour?
Baker's math sets total flour to 100 percent and every other ingredient relative to it. This makes scaling, comparing, and adjusting recipes trivial: a 75 percent hydration loaf doubles in size with one multiplication instead of a fractional rewrite, and two bakers can compare formulas even at different batch sizes.
How does starter hydration affect the math?
A 100 percent hydration starter is half flour and half water by weight. This calculator subtracts that flour and water from the final mix so your true dough hydration stays on target. If you added starter without accounting for it, a 20 percent starter at 75 percent target would actually push you to about 78 percent hydration.
How long should bulk fermentation take?
At 24 Celsius (75 Fahrenheit) with a 20 percent starter, a typical bulk runs 4 to 6 hours until the dough has risen 30 to 50 percent and feels airy. The tool roughly doubles bulk time for every 6 Celsius drop in dough temperature, so an 18 Celsius kitchen may need 8 to 10 hours. Watch the dough, not the clock.
What is the difference between a poolish, a biga, and a levain?
A poolish is a 100 percent hydration preferment, classically yeast-based and very loose. A biga is a stiff Italian preferment around 50 to 60 percent hydration. A levain is a sourdough preferment built from mature starter. All three develop flavor and strength ahead of the final mix; the tool splits flour and water correctly for whichever you choose.
Why is my dough never the hydration the recipe says?
Most home flours absorb 2 to 5 percent less water than commercial bread flour, and whole grains absorb more. Start with the calculated water, hold back 5 percent, and add the rest only if the dough feels too stiff after mixing. Different brands of the same flour vary surprisingly, so treat the number as a well-calibrated starting point.
