Sourdough Calculator

Background.

A recipe calls for 1,000 g of flour at 75% hydration with a 20% levain. The obvious reading is to weigh out 1,000 g of flour and 750 g of water, then stir in 200 g of levain. Do that and the dough is wetter than the recipe intended: a levain fed with equal weights of flour and water brings 100 g of each, so the loaf actually holds 850 g of water to 1,100 g of flour, which is 77.3% hydration, and the batch is 200 g heavier than planned.

Published sourdough formulas avoid this by counting the levain's flour and water inside the totals. King Arthur Baking puts the rule in one line, that everything in the loaf you place in the oven counts as part of the loaf, and gives the split for a 100% hydration starter: 150 g of it contributes 75 g of flour and 75 g of water. Working that way, the same recipe means 900 g of flour and 650 g of water into the bowl, plus 20 g of salt and the 200 g of levain, for 1,770 g of dough.

The split depends on how you keep your starter. A stiff starter fed at 50% hydration is two-thirds flour; a liquid levain at 125% is less than half. Enter your own starter hydration and the calculator divides the levain accordingly, subtracts it from the totals and gives the four weights to put on the scale. It also reports the figures that sourdough writing uses and that are easy to confuse: overall hydration for the whole loaf, mix hydration for what is in the bowl before the levain goes in, and prefermented flour, the share of all the flour that is already fermenting when you mix. You can start from a total flour weight, from the dough weight you want, or from the levain you have already built.

What is sourdough calculator?

Sourdough formulas are written in baker's percentages: total flour is 100% and every other ingredient is a percentage of its weight. The same notation appears in the US federal standard for bread, which sets ingredient limits as parts for each 100 parts by weight of flour. The levain, a portion of active starter built up for one bake, is both a leavening and a share of the flour and water. Overall hydration is total water divided by total flour with the levain's flour and water counted in both, and it is the figure recipes mean. King Arthur describes 55-65% as a firm or stiff dough and 75-85% as slack or sticky, with anything above 80% counted as high hydration. Mix hydration is the water you pour divided by the flour you weigh, before the levain goes in. Prefermented flour is the levain's flour as a percentage of total flour.

How to use this calculator.

1. 01Choose what you are starting from: a total flour weight when you are following a published formula, a target dough weight when you know the batch you want, or the levain you already have when your build is ripe and you want the batch to fit it.
2. 02Enter that one weight in grams. Total flour means all of it, including the flour inside the levain; a dough weight is flour, water and salt for the whole batch before baking.
3. 03Set Overall hydration, Levain (% of total flour) and Salt (% of total flour) from your recipe. Levains of 15% to 25% are ordinary for a 100% hydration starter. Whole wheat and rye absorb more water than white flour, so the same hydration feels firmer with them.
4. 04Set Starter hydration to the way you actually feed your starter: water divided by flour at feeding, times 100. Equal weights of each is 100%.
5. 05Enter the Number of loaves. It only divides the batch; no weight or percentage changes.
6. 06Weigh out the flour, water, salt and levain shown, and use the hydration check line to see the division behind the overall figure.

The formula.

Everything starts from total flour F. The levain weighs L = F × p, where p is the levain percentage divided by 100. A starter kept at hydration q holds q grams of water for every gram of flour, so the levain contains Lf = L ÷ (1 + q) of flour and L × q ÷ (1 + q) of water. Total water is F × h and salt is F × s, with h and s the hydration and salt percentages divided by 100.

The bowl weights are the totals minus what the levain already carries: flour into the bowl F_add = F − Lf, and water into the bowl W_add = F × h − L × q ÷ (1 + q). The dough weighs D = F × (1 + h + s), with no separate term for the levain, because its flour is already inside F and its water already inside the water total. The two other starting points simply find F first: from a dough weight, F = D ÷ (1 + h + s); from a levain on hand, F = L ÷ p.

Two ratios follow. Prefermented flour is Lf ÷ F, which reduces to p ÷ (1 + q). Mix hydration is W_add ÷ F_add; it falls below overall hydration when the starter is wetter than the dough, rises above it when the starter is stiffer, and matches it when the two are the same.

A large or wet enough levain makes a formula impossible. Water into the bowl reaches zero when p × q ÷ (1 + q) = h, and flour into the bowl reaches zero when p ÷ (1 + q) = 1. Zero water is accepted, as a dough made from levain and flour alone; past either edge the calculator stops and names the input to change. The levain is treated as flour and water only, so the small seed of mature starter used to build it is not counted separately, a difference of a fraction of a percentage point at normal seed sizes. Hydration counts added water only: US rules allow flour to hold up to 15% moisture, and no hydration figure includes it.

A worked example.

Frequently asked questions.

References& sources.

1. [1]King Arthur Baking Company. "Hydration in bread dough, explained." Blog post dated 11 January 2023; retrieved 30 July 2026. The primary source for this page's central rule — "Everything that comprises the loaf you place in the oven should be considered as part of the loaf" — and for the levain split at 100% hydration: "a 150 g starter contributes 75 g flour and 75 g water". Also the source of the worked example this calculator reproduces: all-purpose flour 400 g + whole wheat 50 g + rye 50 g + water 375 g + a 100 g sourdough preferment consisting of 50 g flour and 50 g water, giving total water 425 g, total flour 550 g and hydration 425 ÷ 550 = 77%. The band figures quoted in the hydration hint (55-65% firm or stiff, 75-85% slack or sticky, above 80% high hydration) come from the same article.
2. [2]King Arthur Baking Company. "What is baker's math, and how can I use it in my everyday bread baking?" Blog post dated 28 April 2022; retrieved 30 July 2026. Source of the underlying notation this page extends: "the total weight of flour is always treated as 100%" with every other ingredient expressed as a percentage of it, and the total formula percentage as the factor converting a flour weight into a dough weight — the identity behind D = F x (1 + h + s) and its inverse.
3. [3]King Arthur Baking Company. Ingredient Weight Chart, current revision; retrieved 30 July 2026. Cited for the figure that forces this page to be mass-only: "Sourdough Starter — 1 cup: 8 to 8 1/2 ounces / 227 to 241 grams", a 6% spread inside a single published value. Also the source of the salt figures quoted in the hints (table salt 1 tablespoon = 18 g, Morton's kosher 16 g, Diamond Crystal kosher 8 g) and of all-purpose flour at 120 g per cup.
4. [4]U.S. Government Publishing Office / U.S. Food and Drug Administration. 21 CFR § 137.105, "Flour", 2023 annual edition; retrieved 30 July 2026. Quoted for the moisture provision — "Its moisture content is not more than 15 percent." — which is the basis of the page's stated limitation that hydration counts added water only: flour as purchased may legally carry up to 15% of its weight as water, and no hydration figure in any source includes it.
5. [5]U.S. Government Publishing Office / U.S. Food and Drug Administration. 21 CFR § 136.110, "Bread, rolls, and buns", 2023 annual edition; retrieved 30 July 2026. Cited for the point that expressing ingredients as a percentage of flour weight is the notation of federal law and not merely of recipe writing: every optional-ingredient limit in the standard of identity is written as parts "for each 100 parts by weight of flour used" — nonwheat flours at not more than 3 parts, monocalcium phosphate at 0.75 part, dough strengtheners and conditioners at 0.5 part.
6. [6]Hamelman, Jeffrey. Bread: A Baker's Book of Techniques and Recipes. John Wiley & Sons. Cited bibliographically for the prefermented-flour percentage metric — the share of a formula's total flour carried in the preferment — and for the subtract-the-levain method that this page's flour-into-the-bowl and water-into-the-bowl outputs implement, together with the 125% liquid-levain hydration referenced in the starter-hydration hint. PRINT reference: no online full text exists, so no URL is given rather than linking to a third-party reproduction. Access: print.