Someone hands you a recipe that says 75% hydration, you weigh everything to the gram, and the dough comes out noticeably wetter than the video you were following. Nothing was mismeasured. Sourdough hydration explained properly includes a step that most published recipes quietly skip, and once you see it you cannot unsee it: the flour and water inside your levain count.
That single omission is worth two to three percentage points on a typical loaf, and more if you use a big levain. It is also why two bakers can follow the same recipe, both get it right, and end up with doughs that behave differently.
The rest of it is arithmetic you can do on a phone. Total water divided by total flour. That is the whole formula, and the difficulty is entirely in deciding what counts as total.
What hydration actually buys you is a different question, and a more interesting one. 65%, 75% and 85% are not three settings on the same bread. They are three different breads that happen to share a recipe format.
The short answer
Hydration is the weight of water expressed as a percentage of the weight of flour. 500g flour and 375g water is 75% hydration, because 375 divided by 500 is 0.75. Everything in a baker’s percentage recipe is measured against total flour, which is always 100%.
The catch is the levain. It is flour and water too, so both halves belong in your totals. Take 500g flour, 375g water and 100g of a 100% hydration levain. That levain is 50g flour and 50g water, so your real totals are 550g flour and 425g water, and your real hydration is 425 ÷ 550 = 77.3%, not 75%.
Use a stiff levain at 50% hydration instead and the same recipe lands at 72.1%. Same printed number, five points of difference in the dough.
Baker’s percentage from first principles
Every ingredient is stated as a percentage of the total flour weight. Flour is 100% by definition. If there are two flours, they add up to 100% between them.
A standard country loaf:
| Ingredient | Baker’s % | Grams |
|---|---|---|
| Strong white flour | 90% | 450g |
| Wholemeal flour | 10% | 50g |
| Total flour | 100% | 500g |
| Water | 75% | 375g |
| Levain (100% hydration) | 20% | 100g |
| Salt | 2% | 10g |
| Total dough | 197% | 985g |
Two things people find odd at first. The percentages add up to well over 100, which is correct and expected. And salt at 2% sounds trivially small until you realise it is 10g in a loaf, which is exactly the amount that makes bread taste like bread rather than like paste.
Why bother with percentages instead of just writing grams? Because they make a recipe portable. Once you know a formula is 75% water, 20% levain and 2% salt, you can bake it at any size, compare it directly to any other formula, and diagnose what changed when a bake goes wrong. Grams alone tell you nothing about the relationships.
To go from percentages to grams: pick your total flour weight, then multiply. 700g of flour at 78% hydration is 700 × 0.78 = 546g of water. To go the other way, divide: 546 ÷ 700 = 0.78. If you would rather not do this in your head every time, a percentage calculator handles it in one line.
The levain problem: your 75% is not 75%
Here is where recipes get sloppy, and I do not entirely blame them, because the convention of quoting hydration excluding the levain is genuinely widespread and everyone knows what it means. The trouble is that it stops being harmless as soon as you compare two recipes with different levain sizes or different levain hydrations.
A levain is not an ingredient like salt. It is pre-fermented flour and water, and both components are doing exactly what the flour and water you add straight from the bag are doing.
The split formula
For a levain of mass M at hydration h (expressed as a decimal, so 100% is 1.0):
- Flour in the levain = M ÷ (1 + h)
- Water in the levain = M × h ÷ (1 + h)
For a 100% hydration levain, h = 1.0, so the flour is M ÷ 2 and the water is M ÷ 2. Half and half. That is the one you will use most.
For a stiff levain at 50% hydration, h = 0.5, so the flour is M ÷ 1.5 = 0.667M and the water is 0.5M ÷ 1.5 = 0.333M. Two thirds flour, one third water.
Then:
True hydration = (added water + levain water) ÷ (added flour + levain flour)
Worked, end to end: what a printed 75% recipe really is
Say Jonah has the country loaf above. 450g strong white, 50g wholemeal, 375g water, 100g levain at 100% hydration, 10g salt. The header says 75%.
Step one, split the levain. M = 100g, h = 1.0.
- Levain flour = 100 ÷ 2 = 50g
- Levain water = 100 × 1.0 ÷ 2 = 50g
Step two, add those into the totals.
- Total flour = 450 + 50 + 50 = 550g
- Total water = 375 + 50 = 425g
Step three, divide.
- 425 ÷ 550 = 0.7727, so 77.3% true hydration
Step four, while you are here, recheck the other percentages against total flour rather than added flour.
- Salt: 10 ÷ 550 = 1.82%, which is under the usual 2%. To hit 2% properly you want 11g.
- Levain: 100 ÷ 550 = 18.2% of total flour, even though the recipe called it 20%.
- Whole grain: 50 ÷ 550 = 9.1%, not 10%.
None of those gaps is disastrous on its own. Together they are the reason your loaf tastes slightly flatter and behaves slightly wetter than the one in the photograph. And the effect scales: a recipe using a 30% levain shifts hydration by more than one using 15%.
Designing to a true hydration instead
Working forwards is easier than correcting backwards, and it is what I would do if you are building your own formula rather than following someone else’s.
Decide three numbers first: total flour, true hydration, and levain as a percentage of total flour. Then work out what to actually put in the bowl.
Suppose Jonah wants a genuine 75% at the same 550g of total flour, with a 20% levain at 100% hydration.
- Total water = 550 × 0.75 = 412.5g
- Levain mass = 550 × 0.20 = 110g
- Split the levain: 55g flour, 55g water
- Flour to weigh out = 550 − 55 = 495g
- Water to weigh out = 412.5 − 55 = 357.5g, so call it 358g
- Salt at 2% of total flour = 11g
Sanity check the printed figure that would result: 358 ÷ 495 = 72.3%. So a recipe that genuinely delivers 75% would be written as “72% hydration” under the loose convention. That inversion is worth sitting with for a second, because it explains a lot of arguments in baking forums.
Scaling it to the loaf you actually want
Total dough weight = total flour + total water + salt. Here that is 550 + 412.5 + 11 = 973.5g, which bakes down to roughly 866-886g after the oven drives off moisture, since a lean loaf typically loses somewhere around 9-11% of its weight in the bake.
Say Jonah’s banneton suits a 750g dough. Here is the walkthrough.
- Work out the scale factor: 750 ÷ 973.5 = 0.7704
- Scale total flour: 550 × 0.7704 = 423.7g, round to 424g
- Scale total water: 412.5 × 0.7704 = 317.8g, round to 318g
- Scale salt: 11 × 0.7704 = 8.5g
- Levain at 20% of total flour: 424 × 0.20 = 84.8g, round to 85g
- Split the levain: 42.5g flour, 42.5g water
- Flour to weigh: 424 − 42.5 = 381.5g, round to 382g. If you want 10% whole grain, that is 38g wholemeal and 344g white.
- Water to weigh: 318 − 42.5 = 275.5g, round to 276g
- Check your work: 424 + 318 + 8.5 = 750.5g of dough, and 318 ÷ 424 = 75.0% hydration
Nine steps sounds like a lot written down. In practice it is two minutes with a calculator and you only do it once per formula, because from then on you have the grams.
A stiff levain moves the answer by five points
Take exactly the same printed recipe (450g white, 50g wholemeal, 375g water, 100g levain, 10g salt) but build the levain at 50% hydration instead of 100%.
- Levain flour = 100 ÷ 1.5 = 66.7g
- Levain water = 100 × 0.5 ÷ 1.5 = 33.3g
- Total flour = 450 + 50 + 66.7 = 566.7g
- Total water = 375 + 33.3 = 408.3g
- True hydration = 408.3 ÷ 566.7 = 72.1%
77.3% with a liquid levain, 72.1% with a stiff one, from an identical ingredient list. Five points is the difference between a dough you can shape confidently and one that needs a coil fold and a prayer.
There is a flavour dimension too, and this is where bakers genuinely disagree. Stiff levains are often said to favour acetic acid and give a sharper, more complex sourness, while liquid levains favour lactic acid and a milder, yoghurt-like tang. The mechanism is plausible and widely reported by experienced bakers, but the effect in a home kitchen is tangled up with temperature, feeding schedule and flour, so I would not promise you a dramatic difference from the levain hydration alone.
What each hydration band actually feels like
| Hydration | Handling | Crumb | Shaping | Suits |
|---|---|---|---|---|
| 60-65% | Firm, almost stiff, kneads easily | Tight, even, fine | Very easy, holds a tight boule | Bagels, pretzels, sandwich tins, first ever loaf |
| 65-70% | Slightly tacky, cohesive, forgiving | Even and soft with modest holes | Easy, good tension, no stickiness | Beginners, whole grain blends, cold kitchens |
| 70-75% | Tacky, needs a bench scraper | Open enough to look the part, still sliceable | Manageable with dry hands and a light touch | Most home bakers, the practical sweet spot |
| 75-80% | Slack, sticky, wants coil folds | Open, irregular, glossy cell walls | Needs confidence and a fast preshape | Strong flour, decent technique, banneton and retard |
| 80-85% | Very slack, spreads if left alone | Very open, custardy, translucent walls | Difficult, needs lamination or Rubaud mixing | High-protein flour, experienced hands |
| 85%+ | Batter-adjacent, poured rather than shaped | Wild and irregular, wet mouthfeel | Usually tin-baked or ciabatta-style | Specific breads, not a target for a boule |
Those bands assume strong white bread flour at around 12-13% protein. Shift the flour and the whole table shifts with it.
Flour protein, absorption, and why the same recipe changes with a new bag
Absorption is the amount of water a flour can take up and hold. It correlates with protein content, but it is not the same thing, and this is where the standard advice oversimplifies.
Higher-protein flours generally form more gluten and hold more water, so a 13% protein Canadian-blend bread flour will comfortably carry hydration that a 10.5% supermarket plain flour cannot. But milling matters as well. Finely milled flour absorbs faster; coarsely milled or stone-ground flour absorbs more slowly and keeps taking on water for hours. Damaged starch from the milling process absorbs disproportionately. Even storage humidity shifts things by a point or two.
The practical consequence: two bags both labelled “strong white bread flour” can differ by several percentage points of usable hydration. Nobody publishes a reliable absorption figure for retail flour, and I am not going to invent one for you.
What experienced bakers do instead is hold back water. Mix at, say, 68%, let it come together for 20 minutes, then add the remaining 5-7% in stages during the first fold, stopping when the dough tells you to. That technique (a bassinage) is more useful than any table of numbers, because it adapts to whatever is actually in the bag.
One thing to hold steady while you do it: water temperature. Water is also your main lever on dough temperature, and dough temperature drives fermentation speed. The standard three-factor calculation is water temperature = (3 × desired dough temperature) − flour temp − room temp − friction factor. If you are aiming for a 78°F (26°C) dough with 68°F (20°C) flour in a 68°F (20°C) kitchen, that is 234 − 68 − 68 = 98°F (37°C) before friction. Mixing puts heat into the dough, and the friction factor is what you subtract for it: roughly 1-2°F by hand, 4-8°F in a stand mixer or spiral. So hand-mixed doughs want water around 96-97°F (36°C) and machine-mixed doughs nearer 90-94°F (32-34°C). Hand mixing needs the hotter water precisely because it generates less friction, which is the opposite of what most people assume. And if you then change your held-back water to something cold straight from the tap you have quietly altered two variables at once. Use water at the same temperature for the mix and the bassinage.
If you are converting a recipe written in cups or ounces before you do any of this, run it through a unit converter first. Cup measures for flour vary by 20-30g depending on how you scoop, which is enough to move your hydration by four or five points on its own.
Whole grain drinks more, and keeps drinking
Bran and germ absorb considerably more water than endosperm, and they do it over a longer period. A dough at 75% with 20% wholemeal feels drier at mix than the same 75% in pure white flour, and then softens noticeably over the first hour as the bran hydrates.
A working adjustment: add roughly 2-3% extra water for every 10% of whole grain you introduce. So going from all-white to 30% wholemeal at 75%, you would try somewhere around 81-84%. Treat that as a starting point rather than a rule, because a coarse stone-ground wholemeal and a fine commercial one behave differently.
An autolyse helps here more than anywhere. Mixing just flour and water and leaving it 30-60 minutes before adding levain and salt gives the bran time to take up water before you judge the consistency, which stops you adding water you will regret an hour later.
Higher whole grain also ferments faster, so if you raise the whole grain content you should expect to shorten bulk. A 30% wholemeal dough at 78°F (26°C) can finish bulk noticeably sooner than an all-white dough at the same temperature, and if your kitchen also happens to be warm that day, the two effects stack. Running the numbers on that alongside your dough temperature is exactly what the Sourdough Proofing Scheduler is for: it turns a measured dough temperature into a realistic bulk window and a set of clock times, all in your browser with nothing uploaded and no account. If you are fitting the bake around a working day, the Bread Bake Timeline Scheduler does the same job across the whole sequence.
What counts as water, and the arguments about it
In a lean dough of flour, water, levain and salt, this question does not arise. In anything enriched, it does, and there is no settled convention.
Milk is roughly 87% water by weight, so 200g of milk contributes about 174g of water and around 26g of solids. Eggs are roughly 75% water, so a 50g egg contributes about 38g. Counting those gives you a hydration figure that actually predicts how the dough will behave. Ignoring them gives you a number that looks tidy and means less.
Fats are the clearer case. Oil, butter and lard do not hydrate flour. They coat it, shorten the gluten, and soften the crumb, which is why enriched doughs feel supple at hydrations that would be stiff in a lean dough. Almost nobody counts fat as water and I would not either.
Sugar is stranger still, because it is hygroscopic and competes with the flour for water, which is one reason very sweet doughs ferment slowly and feel different. If you are moving an enriched recipe across from commercial yeast, that interaction matters more than the hydration figure does, and it is covered in the conversion arithmetic and timing.
Where I land is this: pick a convention, state it when you share a recipe, and stop arguing about it. The number is a tool for repeating your own results, not a competitive standard.
The advice I would actually give a beginner
Go down, not up.
There is a strong cultural pull towards high hydration in sourdough, because the photographs that circulate are of wildly open crumb, and open crumb comes more easily at 80% than at 68%. So people who have made four loaves try 82%, produce something that spreads across the peel like a pancake, and conclude they need a better starter.
Drop to 68-70% with strong bread flour. Everything gets easier at once. You can shape with tension, the dough tolerates a wider fermentation window before it collapses, the loaf holds its height, and the crumb is even and pleasant to eat. You will not get a crumb full of caverns, and that is fine, because a caverned crumb is a poor vehicle for butter anyway. I would rather eat a well-fermented 70% loaf than a fashionable 85% one nine times out of ten.
Then go up in increments of two or three points, one variable at a time, once you can reliably shape what you have. Keep the rest of the bake constant while you do it, which means holding the same dough temperature and the same bulk window; the proofing scheduler is useful here mainly as a way of not accidentally changing two things at once. If a bake at 75% comes out dense and sticky, hydration might not be the culprit at all, and the way to tell is to read the crumb and the silhouette, which is covered in telling under-proofed from over-proofed.
Where the real problems start
Measuring by volume, first and always. A cup of flour varies enormously with how you fill it, so your hydration is not the number you think it is and cannot be repeated. Scales cost less than a bag of good flour.
Second: comparing recipes without normalising for the levain. A “78%” formula with a 10% liquid levain and an “80%” formula with a 35% liquid levain are not two points apart, they are further apart than that, and in the opposite direction to what you would guess.
Third: raising hydration and whole grain together. Both make the dough slacker and faster, and doing both in one bake gives you a puddle you cannot attribute to either.
Fourth: forgetting that the water in the recipe includes any water you use to wet your hands, dissolve the salt, or add during a bassinage. Small amounts, but they add up and they are invisible in your notes unless you write them down.
Fifth, and this is the one that surprises people: chasing a hydration number that your oven setup cannot support. A very wet dough needs strong steam and a hot start to set the crust before it spreads. If you bake on a tray in a domestic oven without a covered vessel, 80% will spread on you no matter how good your shaping is.
Frequently asked questions
What does 75% hydration mean in sourdough?
It means the water weighs 75% of what the flour weighs. For 500g of flour that is 375g of water. Baker’s percentages are always relative to total flour, which is set at 100%, so the figures across a recipe add up to well over 100. Volume measures cannot express this reliably, so weigh everything on a digital scale.
Does the starter count towards sourdough hydration?
Yes, and this is the step most recipes skip. A levain is flour and water, so both halves belong in your totals. A 100g levain at 100% hydration contributes 50g of flour and 50g of water. Adding those to a printed 75% recipe usually pushes the real figure to around 77%. The larger your levain, the bigger the gap between the printed number and the truth.
How do I calculate hydration with a 100% hydration starter?
Split the levain in half, since equal flour and water is what 100% hydration means. Add half the levain weight to your flour total and half to your water total, then divide total water by total flour. For 500g flour, 375g water and 100g levain that is 425 ÷ 550, which is 77.3%. For a levain at any other hydration h, the flour is M ÷ (1 + h) and the water is M × h ÷ (1 + h).
What hydration should a beginner start at?
Around 68-70% with strong bread flour. That is wet enough for a pleasant open crumb and dry enough that the dough holds a shape you can work with. Most beginners chase 80% too early, get a slack dough they cannot shape, and blame their starter or their fermentation instead of the water. Going down is almost always the faster route to a better loaf.
Why does the same recipe feel wetter with a different bag of flour?
Because absorption varies. Protein content, milling fineness, damaged starch and even storage humidity all change how much water a flour takes up. Two flours both labelled strong white can differ by several percentage points of absorption. The practical answer is to hold back 5% of the water at mix and add it during the first fold, stopping when the dough feels right rather than when the jug is empty.
Do milk, eggs and oil count as water in baker’s percentages?
Bakers disagree, and both conventions are in circulation. Milk is roughly 87% water and eggs roughly 75%, so counting their water content gives a hydration figure that better predicts how the dough behaves. Oil and butter are fats and do not hydrate flour, though they soften the crumb considerably. State which convention you are using whenever you share a recipe, and the argument mostly disappears.
The takeaway
Write down your true hydration once, in a notebook, with the levain counted properly. It takes five minutes and it turns every future bake into a comparison rather than a fresh gamble.
Then treat the number as a description of the bread you want rather than a score. 68% makes an excellent sandwich loaf that slices cleanly and toasts well. 75% makes the loaf most people picture when they say sourdough. 85% makes something custardy and dramatic that will fight you at every stage and be worth it perhaps one bake in three.
If you are stuck, drop five points and bake the same formula again. Almost nobody regrets that, and the loaf that comes out will tell you far more about your fermentation than a slack dough ever could.