Sourdough Hydration Calculator
Splits your levain into the flour and the water it actually contains, so the hydration you write down is the hydration you mixed — and separates prefermented flour from levain weight, which are not the same number.
Sourdough Hydration Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Peak times assume 70 to 75°F; every 17°F roughly halves or doubles fermentation speed.
- Assumes the starter is at the hydration you state and is fully ripe when used.
- Does not model flour absorption, which varies widely between white, whole wheat and rye at the same stated hydration.
- Salt is calculated on total flour and ignores any salt in a salted levain.
In short: A levain at 100% hydration is half flour and half water, so 20% prefermented flour weighs 40% of the flour — and a “20% starter” by weight is only 10% PFF. That factor of two is the most common error in sourdough arithmetic. The second is pouring the recipe’s full water on top of the levain: on a 500 g flour dough at 75%, that turns a correct 275 g of added water into 375 g and the real hydration into 95%.
Formula
prefermented flour = total flour × PFF%
levain = prefermented flour × (1 + starter hydration)
water to add = total flour × hydration − water in levain
flour to add = total flour − flour in levain
at 100% starter hydration: levain weight % = 2 × PFF%
[('PFF', 'Prefermented flour — the share of TOTAL flour fermented in the levain. The quantity worth quoting.'), ('starter hydration', 'Water as a fraction of the flour inside the starter. 100% is equal parts.'), ('levain weight', 'Flour plus water in the levain. Meaningless unless the hydration is stated alongside it.'), ('feeding ratio', 'Seed : flour : water. Controls timing and carried acidity, not the final dough.')]
Worked Example
- Fix the total flour and the target hydration. Both include everything inside the levain.
- Decide the prefermented flour percentage. Twenty percent is the usual default; 10 to 15% for a slow overnight bulk.
- Split the levain into its flour and water. Divide by one plus the starter hydration for the flour; the rest is water.
- Deduct both from the dough totals. Add only the remaining flour and the remaining water to the bowl.
- Build the levain to peak when you need it. The feeding ratio sets the timing, not the bread.
A 500 g flour dough at 75% hydration with a 20% prefermented flour levain at 100% starter hydration needs a 200 g levain, 400 g of added flour and 275 g of added water. Pouring the recipe's full 375 g of water on top of the levain instead takes the real hydration to 95% — twenty points over target, and the difference between a dough you can shape and one that spreads across the bench.
Strengths & Limits Of This Model
Where this engine is strong
- Separates prefermented flour from levain weight, which recipes conflate
- Deducts the levain's own water so the stated hydration is the real one
- Accepts all three ways recipes specify a preferment
- Shows that feeding ratio changes timing and carried acidity, not the bread
Where it stops
- Peak times are temperature-dependent estimates, not guarantees
- Cannot account for the vigour of an individual culture
- Flour absorption differences are outside the arithmetic
Practical Use Cases
Converting a recipe between starter hydrations
Keep the prefermented flour fixed and only the added water changes; the dough is identical.
Working out what a recipe means by “20% starter”
It is 10% prefermented flour if the figure is by weight and 40% of flour weight if it is PFF — a factor of two.
Scheduling a bake around when the levain peaks
Choose the feeding ratio that peaks when you want to mix, not the one the recipe happens to use.
Diagnosing a dough that was far wetter than expected
Usually the levain's own water was added twice, which on a typical formula is worth twenty points of hydration.
Methodology & Editorial Standards
The calculation treats the levain as what it physically is: flour and water mixed in advance. Its flour content is the levain weight divided by one plus the starter hydration expressed as a decimal, and the remainder is water. Both are then deducted from the dough's totals, so the water poured into the bowl is the target hydration times the total flour, less the water already inside the levain. Three input conventions are accepted and reconciled to a single prefermented-flour weight, because recipes use the same language for quantities that differ by a factor of two: prefermented flour as a percentage of total flour, levain weight in grams, and levain as a percentage of flour weight. At 100% starter hydration the third is always exactly double the first. Inoculation bands and their bulk-fermentation times follow the ranges published by The Perfect Loaf and the broader sourdough literature: 10 to 15% for a mild slow ferment, 18 to 22% as the general-purpose band, 25 to 30% for a fast same-day bake. Feeding-ratio peak times are given at 70 to 75°F and the seed carryover is derived as the reciprocal of the build multiple, which is what actually distinguishes the ratios in flavour terms. The page states explicitly that the feeding ratio does not alter the finished dough, only the timing and the carried acidity.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Sourdough Hydration Calculator — 20 Expert FAQs
20 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How do I include starter in hydration calculations?
Split it. A starter at 100% hydration is exactly half flour and half water, so 200 g of it is 100 g of flour and 100 g of water, and both go into the dough totals — the flour into the denominator, the water into the numerator. Then subtract each from what you add to the bowl. Treating the starter as a wet ingredient understates the flour and overstates the water simultaneously, which doubles the error.
What is PFF in sourdough?
Prefermented flour: the percentage of the recipe's total flour that is already fermenting in the levain. It is the only preferment figure that means the same thing regardless of how wet your starter is, which is why professional formulas quote it. Twenty percent is the common default, 10 to 15% gives a slow overnight bulk, and 25 to 30% gives a fast same-day one.
Is a 20% starter the same as 20% prefermented flour?
No, and this is the single most common error in sourdough maths. At 100% starter hydration a 20% PFF levain weighs 40% of the flour, because half of it is water. Conversely a levain weighing 20% of the flour is only 10% PFF. Recipes use the same phrasing for both, so a formula read the wrong way gives you either double or half the preferment you intended.
Does the feeding ratio change how sour my bread is?
Less directly than people assume. The ratio sets when the levain peaks — 1:1:1 in four to six hours, 1:10:10 in fourteen to twenty. What it genuinely changes is carried acidity: at 1:1:1 a third of the ripe levain is the previous acidified build, against 9% at 1:5:5. Sourness is driven far more by fermentation temperature and by how ripe the levain is when you use it.
Can I use any feeding ratio for the same recipe?
Yes. Any build that reaches the same levain weight at the same ripeness produces the same dough. The ratio is a scheduling tool: choose the one that peaks when you want to mix. A 1:1:1 build suits a bake you start the same afternoon; a 1:5:5 or 1:10:10 build is what you feed at night to find a ripe levain in the morning.
How much starter should I use for 500 g of flour?
About 200 g at the common 20% prefermented flour with a 100% hydration starter, which is 100 g of flour and 100 g of water. If you want a slower, more forgiving overnight bulk, drop to 10 to 15% PFF, which is 100 to 150 g of levain. If you want to bake the same day, go to 25 to 30%, which is 250 to 300 g, and watch the dough closely.
What is the difference between stiff and liquid levain?
Only the water in it, and the consequences of that. A stiff levain at 50 to 60% hydration ferments more slowly and favours acetic acid, giving a sharper, more vinegary flavour and a stronger gluten network. A liquid levain at 100% or more is faster and more lactic, giving a milder, yoghurt-like tang. Keep the prefermented flour the same and the bread's structure barely changes; the flavour does.
Why is my sourdough so much wetter than the recipe says?
In most cases the levain's water was counted twice — the full recipe water went in on top of a levain that already contained water of its own. On a 500 g flour dough at 75% with a 200 g levain, that takes the real hydration from 75% to 95%. The second common cause is flour: whole wheat and rye absorb far more water than white, so the same percentage handles quite differently.
Does starter hydration change my dough hydration?
It changes what you pour, not what you end up with, provided you do the arithmetic. Hold the prefermented flour constant and switch from a stiff 50% levain to a liquid 100% one, and the levain weight rises from 150 g to 200 g while the water you add falls from 325 g to 275 g. The finished dough is identical at 75%. That is precisely why prefermented flour is the figure worth recording.
How long should my levain take to peak?
At 70 to 75°F, roughly 4 to 6 hours at 1:1:1, 6 to 8 at 1:2:2, 8 to 10 at 1:3:3, 10 to 14 at 1:5:5 and 14 to 20 at 1:10:10. Flour shifts this: bread flour adds 30 to 60 minutes, whole wheat runs 20 to 30% faster and rye 30 to 50% faster. Use the dome and the smell rather than the clock — a levain that has peaked and started to fall has already passed its best.
Is this sourdough hydration calculator free to use?
Yes. It is free, requires no account, and has no usage limits. ApexConverter is funded by contextual advertising, never by selling user data.
Is my data sent to a server?
No. The engine runs as Vanilla JavaScript inside your browser under our Zero-Server Client-Side Execution model. Your figures are computed locally and are never transmitted, logged, or stored.
How accurate is this calculator?
It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.
Does it work on mobile?
Yes. The interface is mobile-first with numeric keypad hints and is tested down to a 320-pixel viewport with no horizontal scrolling.
Can I use it offline?
Largely, yes. Because computation is client-side, the page continues to calculate without a network connection once it has loaded.
Which currency does it use?
Amounts display in US$ accounting format, but the underlying mathematics is currency-agnostic. The result is identical in any currency, so simply read the figures in your own.
Why does a result show an em-dash?
An em-dash indicates the calculation is not defined for the inputs given — typically a division by zero or a value outside the valid domain. We show a dash rather than a misleading number.
How do I report an error?
Email apexconverter.praxiscalc@gmail.com with the tool URL, your exact inputs, the output received and the output you expected. Verified mathematical errors are patched within 72 hours.
Where can I find related sourdough hydration calculator tools? (1)
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Where can I find related sourdough hydration calculator tools? (2)
Use the Related Engines panel on this page, or open the category hub for all 50 tools.