Sourdough Calculator

Calculate sourdough flour, water, salt, and starter from loaf weight, hydration, prefermented flour percentage, and starter hydration, then split the formula into starter-build and final-mix grams.

Last updated 26 March 2026

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Sourdough calculator: starter build, hydration, inoculation, and final-mix dough weights

A sourdough calculator uses baker’s percentages to turn a target loaf weight into total flour, water, and salt, then splits that formula into the starter build and the final mix. The extra step, compared with a standard bread calculator, is that sourdough starter already contains flour and water, so the calculator has to back those amounts out of the final dough correctly.

About this calculator

Reviewed 2026-03-26

Methodology

Calculates total flour, water, and salt from loaf count, target dough weight, hydration, and salt percentage, then allocates a user-defined prefermented-flour share into the starter build and subtracts the starter’s flour and water from the final mix according to the entered starter hydration.

Limitations

Models dough composition only and does not predict fermentation time, dough temperature, shaping strength, or oven spring.
Treats the entered starter percentage as prefermented flour rather than total starter weight.
Baked-yield output is an estimate based on representative moisture loss rather than a measured bake profile.
Does not adjust automatically for whole-grain absorption, add-ins, or salt and hydration targets outside the entered ranges.

Disclaimer

Use this calculator as a sourdough planning aid only. Final fermentation timing, dough feel, and bake performance still need judgement based on flour choice, starter strength, room temperature, and handling.

Sources

King Arthur Baking - Sourdough Baking Guide — Foundational sourdough reference covering starter behaviour and baking workflow.
The Perfect Loaf - Beginner's Sourdough Bread — Detailed sourdough guide explaining hydration, starter quantity, and process choices.
The Perfect Loaf - Baker Notes — Reference notes on baker’s percentages, levain builds, and batch planning.

See our calculation methodology and editorial standards for how this estimate is produced.

How prefermented flour and starter hydration work

This calculator treats the starter percentage as prefermented flour. If you set prefermented flour to 20%, then one-fifth of the total flour in the dough sits inside the starter build before you mix the final dough.

Starter hydration changes how much of that starter build is flour versus water. A 100% hydration starter contains equal flour and water by weight. A stiffer or looser starter changes the split and therefore changes how much extra water you add in the final mix.

Total flour = Total dough / (1 + Hydration + Salt)

Hydration and salt percentages are expressed as baker’s percentages relative to flour.

Starter flour = Total flour x Prefermented flour

The selected prefermented-flour percentage determines how much flour lives inside the starter build.

Starter water = Starter flour x Starter hydration

The starter contributes both flour and water, so the final mix must subtract both quantities.

Worked example: one 900 g loaf at 75% hydration

Suppose you want one 900 g loaf at 75% hydration, 2% salt, 20% prefermented flour, and a 100% hydration starter. The calculator produces about 508.5 g total flour, 381.4 g total water, and 10.2 g salt.

With 20% prefermented flour, the starter build uses about 101.7 g flour and 101.7 g water for roughly 203.4 g of starter. The final mix then takes the remaining 406.8 g flour, 279.7 g water, and 10.2 g salt.

How to use the result in practice

The starter-build output is a planning aid: it tells you how much ripe starter you want ready before the final mix begins. The final-mix output then tells you the remaining flour, water, and salt to combine with that mature starter.

Treat the baked-yield number as an estimate, not a guarantee. Actual baked weight depends on crust darkness, steam, bake duration, and how much moisture your loaf loses in the oven.

Sourdough Calculator

Sourdough calculator: starter build, hydration, inoculation, and final-mix dough weights

How prefermented flour and starter hydration work

Worked example: one 900 g loaf at 75% hydration

How to use the result in practice

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