Sourdough Hydration Calculator (True Hydration)

Your recipe says 70% hydration. Your dough feels like 76%. The calculator you used is probably lying to you, and it's not your fault. Most of them forget that your starter is half flour and half water, and that missing math is why your crumb keeps coming out tighter than the photo in the recipe.

What hydration actually means

In baking, hydration is just water as a percentage of flour weight. That's the whole idea behind baker's percentage: you pick a flour weight as your base (100%), and everything else is a ratio of that number.

So if you have 500g of flour and 375g of water, your hydration is:

Simple enough. The trouble starts when you add a starter to the mix, because a starter isn't just "a liquid thing you add." It's a mixture of flour and water, and if you treat it as a single ingredient, you're quietly throwing off your numbers.

Calculator

Run this in the calculator

basic bread hydration calculator. Enter flour weight and water weight, outputs hydration percentage.

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Why most sourdough hydration calculators are wrong

Here's a recipe a lot of home bakers follow without thinking twice:

• 500g bread flour
• 350g water
• 250g starter (at 100% hydration)
• 10g salt

You punch the flour and water into a calculator. 500g flour, 350g water. It spits out 70%. Feels right. Matches the blog post. You move on.

But that 250g of 100% hydration starter is not invisible. A 100% hydration starter is fed equal weights of flour and water, so it's literally half and half. That 250g breaks down into:

• 125g flour (from the starter)
• 125g water (from the starter)

Now your real numbers are:

• Total flour: 500g + 125g = 625g
• Total water: 350g + 125g = 475g

That's a six-point gap. On paper it looks small. In the bowl, 70% and 76% feel meaningfully different. One holds its shape during shaping. The other wants to spread. And if you're chasing an open crumb or struggling with an overproofed slack dough, that gap is often the culprit.

This is what bakers call nominal hydration (what the simple math says) versus true hydration (what's actually in your dough). Most sourdough hydration calculators online only give you the nominal version, which is exactly why the number on the screen stops matching the feel of the dough.

Calculator

Run this in the calculator

true hydration calculator with starter decomposition. Fields for added flour, added water, starter amount, and starter hydration percentage. Outputs true hydration with a full breakdown showing flour from starter, water from starter, total flour, total water.

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How to split a starter into flour and water

The math is friendlier than it looks. If your starter is at 100% hydration, splitting it is easy: half the weight is flour, half is water.

For any other hydration, the formula is:

Say you're using 200g of an 80% hydration stiff starter:

Compare that to the same 200g at 100% hydration (100g flour / 100g water), and you can see why switching starter types quietly shifts your dough hydration even when nothing else in the recipe changes.

The shortcut for 100% starters: just divide by two. For stiff starters, the formula above takes about 30 seconds. Or use the starter hydration calculator above, which handles any starter hydration automatically.

Not sure what hydration your starter is? Learn about starter hydration and how to adjust it.

Seeing where everything comes from

Once you break down every ingredient, the picture gets clearer: your dough's hydration isn't coming from one place. It's coming from two places. The water you added directly, and the water that arrived inside your starter.

Using the earlier example with 500g flour, 350g water, and 250g of 100% hydration starter, the starter is contributing 20% of the total flour and about 26% of the total water in your dough. That is not a rounding error. That is a real chunk of your formula arriving pre-mixed.

Starter flour

125g

Added flour

500g

Flour

625g total

Starter water

125g

Added water

350g

Water

475g total

Seeing it this way makes it obvious why starter size matters so much. A recipe with 300g of starter has a lot more phantom flour and phantom water than one with 100g. Scale up the starter, scale up the gap between nominal and true hydration.

Why this number actually matters

Six percentage points sounds minor. In practice, it can change the whole bake.

Dough feel and handling. A 70% dough and a 76% dough behave differently in your hands. The higher-hydration dough is stickier, spreads faster on the bench, and needs more confident, decisive shaping. If you're fighting with a dough that keeps spreading during shaping, and the recipe said "this is a manageable 70%," check whether the true hydration is quietly sitting in the mid-to-upper 70s.

Oven spring and open crumb. Higher hydration generally helps with oven spring, up to a point. The steam inside the dough has more to work with. But if the structure isn't there to hold it, you get spread instead of rise. True hydration helps you diagnose whether a flat loaf is a structure problem or a hydration-that-was-actually-higher-than-you-thought problem.

Consistency between bakes. If you calculate true hydration once and write it down, you can actually reproduce your dough. Nominal hydration is technically a different number every time your starter amount changes, even if the flour and water additions stay the same.

If you want to rebuild a recipe around a specific true hydration target, the full recipe calculator can work backwards from there.

Hydration and flour choice

Here's something the percentage alone can't tell you: 75% hydration doesn't feel the same across different flours.

Bread flour has a higher protein content, which means it absorbs more water before the dough gets slack. A 75% bread flour dough can feel quite firm. The same 75% with all-purpose flour feels noticeably softer and stickier, because all-purpose absorbs less.

Whole wheat and rye take it further. Whole grain flours absorb significantly more water because the bran soaks it up. If you swap even 20% of your bread flour for whole wheat and keep everything else the same, your dough will feel tighter, even though the percentage is identical.

This is why "don't conflate hydration with wetness" is real advice. The number tells you the ratio. The flour tells you what that ratio actually feels like. Two bakers can be at the same true hydration and have very different experiences depending on what's in their bags.

Target hydration by bake style

These are ranges, not rules. Your flour, your kitchen temperature, and your experience level all play a role. But if you're starting from scratch and wondering what to aim for, this is a reasonable starting point.

These ranges assume true hydration, not nominal. If you're comparing your recipe against them, make sure you're comparing the same number.

A beginner baking their first sourdough boule is going to have a much easier time at 72% than at 80%, even if 80% produces a better crumb. Get comfortable with the process first, then push the hydration up once shaping stops being a battle.

When the sourdough hydration calculator is overkill

Not every bake needs this level of precision. Here's when you can safely ignore it:

Your starter amount is small. If you're using 50g of starter in a 1000g flour recipe, the starter contributes about 25g of flour and 25g of water. That shifts your true hydration by under a percentage point. Often not worth worrying about.

You've made this recipe many times. You've already internalized how the dough should feel. The true hydration calculator is most useful the first time through a recipe, or when something feels off and you're trying to figure out why.

It's a quick weeknight bake and you're not chasing perfection. Sometimes you just want bread. Nominal hydration is good enough for that. It's when you're trying to dial in a specific result, like an open crumb, a thinner crust, or a dough that shapes without sticking, that the true number starts to matter.

When does nominal bite you? When your starter percentage is high (20-25% or more of total flour), when you're comparing a recipe to someone else's notes and trying to figure out why yours came out different, or when you're troubleshooting a dough that consistently underperforms.

Stiff starters and liquid levains

If you keep a stiff starter at 50% or 65% or 80% hydration, you already know that starter behavior is completely different from a 100% liquid levain. But the hydration math is also different in a way that catches people off guard.

A 200g addition breaks down very differently depending on starter style:

• 200g of 50% stiff starter → 133g flour, 67g water
• 200g of 100% liquid starter → 100g flour, 100g water
• 200g of 125% very liquid levain → 89g flour, 111g water

Same starter weight. Three very different effects on the dough. This is exactly why calculators that assume every starter is at 100% hydration are barely better than calculators that ignore starter entirely.

If you swap your liquid levain for a stiff starter without adjusting your added water, your dough will come out noticeably tighter than it should be. The fix is simple: use the starter decomposition calculator above, see what your starter actually contributes, and adjust your added water to hit your target true hydration.

More on keeping and adjusting starter hydration.

One more thing

Once you know your true hydration, you might realize the recipe you've been following needs tweaking. If you want to scale it up for a bigger loaf, or rebuild the formula from a different flour weight, the full recipe calculator handles all of that in one place. And if you're trying to resize a recipe you already trust, the recipe scaler can adjust quantities without breaking the ratios.

The math isn't complicated once you see it. The starter is just flour and water. You just have to count it.