Sourdough Hydration Calculator

Plan a sourdough bake around total flour, then see how much of that flour and water the levain already supplies. The page returns a two-column recipe: the overall target and the amounts left to mix by hand.

Total Flour First, Levain Second

This tool is built around a single anchor: the total flour in the dough. Hydration, salt and levain are all percentages of that total, which is the standard baker's-percentage convention. The important twist is that the levain is not treated as an extra ingredient. Part of your total flour and total water arrives inside it, so the calculator subtracts those amounts and reports what is left to add to the bowl.

• The levain is split according to its own hydration. At 100 percent, a 100 g levain is 50 g flour and 50 g water; at 75 percent it is about 57 g flour and 43 g water; at 125 percent roughly 44 g flour and 56 g water.
• Because levain flour comes out of the flour total, the flour you actually weigh is less than the headline figure. A 500 g target with a 20 percent levain leaves 450 g of flour to add.
• The same subtraction applies to water. A 75 percent hydration target on 500 g is 375 g of water in total, but the levain contributes some of it, so the jug is filled to a lower number.
• Salt is the one ingredient that is not divided. It is simply two percent of total flour and is added in full at the mixing stage.

Running the Recipe and the Feed

1. Enter the total flour weight for the bake you have in mind, not the flour you will tip into the bowl. This is the number every percentage refers to.
2. Set the target hydration. Sourdough commonly sits between 70 and 80 percent, and the default is 75.
3. Choose salt and levain percentages. Twenty percent levain is a common starting point and two percent salt is typical.
4. Pick the levain's own hydration from the dropdown so the tool knows how much flour and water are riding along inside it.
5. Press Calculate Recipe for the two-column breakdown, or press Starter Feeding if what you actually need is how to refresh the jar before mixing.

Default Bake, Both Buttons

With the tool untouched at 500 g flour, 75 percent hydration, 2 percent salt, 20 percent levain at 100 percent hydration and one loaf, the recipe panel reports the following.

• Total flour 500 g, of which 450 g is weighed out; the remaining 50 g arrives inside the levain.
• Total water 375 g, of which 325 g is poured; the other 50 g comes from the levain.
• Levain 100 g, described as containing 50 g flour plus 50 g water, and salt 10.0 g added in full.
• The Starter Feeding button reports how to refresh the jar. At the default 100 percent hydration it prints 500 g existing starter, 500 g fresh flour and 500 g water, the familiar one-to-one-to-one feed, and the starter line notes that the 500 g is roughly 250 g flour plus 250 g water.
• The feeding weights follow the dropdown rather than staying fixed. Set it to 75 percent and the water falls to 375 g, with the ratio written as 1:1:0.75; set it to 125 percent and the water rises to 625 g, written as 1:1:1.25. The fresh flour stays at 500 g in every case, so the refreshed jar keeps the hydration you selected.

Three Ways to Think About a Levain

Alternative	Notes
Levain as part of the flour	This is the page's model. The levain is flour and water, both of which count towards the dough's totals, so they are deducted before mixing. It is the most accurate approach and the one most consistent with baker's percentages.
Levain as a separate addition	Some home recipes ignore the flour and water in the starter and simply add it on top. The finished dough then has more flour and water than the headline percentage implies, and the true hydration drifts above the stated target.
Build a dedicated levain	Rather than carrying your jar straight into the dough, you can build a levain the night before at a known ratio built specifically for the bake. This gives tighter control but adds a step and consumes extra flour that the page never sees.
Work backwards from dough weight	If what matters is filling a particular tin, you can fix the total dough weight and derive the flour from it. The page does not do this; it starts from flour and returns dough ingredients, so you would have to iterate.

Local Calculation, Nothing Uploaded

Both panels are produced by JavaScript running in your own browser tab. The tool does not call out to a server to do the sums.

• Flour, water, levain and salt figures are computed on your device from the values you type. No recipe data leaves the page.
• There is no account and no submission step. The two buttons only rewrite the result panel on the same screen.
• After the page has loaded it continues to work with no connection, because nothing in the calculation depends on remote data.
• Your theme choice is stored locally in the browser so it persists on your next visit; nothing else about your session is retained.
• Refreshing the page clears the form back to its defaults, so copy the output you want before you navigate away.

Sourdough Questions

Why is the flour I weigh less than the flour I entered?

Because part of your total flour is already sitting in the levain. At 20 percent levain and 100 percent hydration, the 100 g of starter is half flour and half water, so 50 g of flour is contributed before you open the flour bag. The calculator deducts it and shows both the full total and the to-mix amount so you can see where every gram goes.

Does the levain hydration change the recipe amounts?

It changes how the levain is split, and therefore how much flour and water you add by hand, but not the dough's overall totals. A stiffer levain carries more flour and less water, so you add less flour and more water later. The finished dough reaches the same hydration either way; only the mixing quantities differ.

What ratio does the feeding button actually use?

It feeds one part existing starter to one part fresh flour, with the water set by the starter's own hydration, so the refreshed jar keeps whichever hydration you chose in the dropdown. At 100 percent the water equals the flour and you get the classic one-to-one-to-one feed; at 75 percent you add three-quarters as much water and the panel writes the ratio as 1:1:0.75; at 125 percent you add a quarter more, shown as 1:1:1.25. The existing-starter line also spells out how that starter splits into its own flour and water, so you can see where the fresh amounts come from.

How much levain should I use?

It depends on timing and temperature more than on the recipe. A higher levain percentage ferments faster and gives less sourness; a lower percentage slows the rise and develops more flavour. Twenty percent is a reliable middle ground for an overnight bulk at room temperature, and you can shift it as you learn how your starter behaves.

Last verified: October 3, 2026

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Maintained by Huang Bin · Last updated October 3, 2026