How to Calculate Sourdough Hydration as Baker's Percentage

A sourdough recipe calls for a specific hydration percentage — “75% hydration dough” — and you’re trying to figure out exactly how much water that translates to for your specific flour quantity, especially once your starter (which itself contains both flour and water) is factored into the total. Baker’s percentage math isn’t complicated in principle, but getting it right consistently, especially once starter is part of the equation, is easy to fumble without actually working through the calculation deliberately.

Hydration percentage is one of the most useful numbers in sourdough baking precisely because it’s a ratio, not an absolute quantity — it lets you scale a recipe up or down, or compare different recipes’ actual wetness, independent of how much total dough you’re making.

What calculating sourdough hydration actually involves

Baker’s percentage expresses every ingredient as a percentage of the total flour weight, with flour itself always defined as 100%. Hydration percentage specifically is total water weight divided by total flour weight, expressed as a percentage — and because a sourdough starter itself is roughly half flour and half water (in a typical 100% hydration starter), the flour and water contributed by the starter need to be added into the totals, not just the water and flour added separately during mixing.

Why people get stuck here

• Forgetting to account for the starter’s own flour and water content. A starter isn’t purely “extra water” — it contains both flour and water in its own ratio, and omitting its contribution from the total flour and water calculation gives an inaccurate hydration figure.
• Confusing hydration percentage with a simple water-to-flour ratio stated differently. Baker’s percentage is specifically water divided by flour, expressed relative to flour as 100% — a subtly different framing than some other ways of describing dough wetness that can lead to confusion when converting between recipe styles.
• Not adjusting water correctly when scaling a recipe. Scaling a recipe up or down while keeping hydration percentage constant means recalculating the actual water quantity needed for the new total flour amount, not simply scaling the original water figure by the same factor as everything else without checking.
• Assuming all sourdough starters have the same hydration. Not every starter is maintained at 100% hydration (equal parts flour and water by weight) — a stiffer or wetter starter changes how much flour and water it actually contributes to the total.

What a good sourdough hydration calculator looks like

Includes starter’s flour and water contribution in the total

Correctly folding the starter’s own flour and water content into the overall calculation, rather than treating it as pure water, gives an accurate hydration percentage.

Computes water needed for a target hydration

Working backward from a desired hydration percentage to the actual water quantity needed for your specific flour amount removes the manual algebra from adjusting a recipe to a target hydration.

Handles starters at different hydration levels

Accounting for a starter’s own hydration (not assuming it’s always exactly 100%) keeps the calculation accurate for bakers maintaining a stiffer or wetter starter than the common default.

Common mistakes to avoid

• Treating starter as pure added water rather than accounting for the flour it also contributes to the total.
• Scaling a recipe’s water quantity by the same multiplier as flour without recalculating for the target hydration percentage specifically.
• Assuming every recipe’s stated “hydration” number uses the exact same baker’s percentage convention without checking.
• Not accounting for your specific starter’s actual hydration level if it differs from the common 100% default.
• Forgetting that other wet ingredients (like an egg or additional liquid in an enriched dough) also count toward total hydration if the recipe includes them.

How to do it with Sourdough Hydration Calculator

Online Tool Store’s Sourdough Hydration Calculator computes your hydration entirely in your browser.

1. Open the Sourdough Hydration Calculator tool.
2. Enter your flour, water, and starter weights (including your starter’s own hydration level).
3. Get your dough’s actual baker’s percentage hydration.
4. Use the target hydration feature to see how much water to add for a specific desired hydration level.

Frequently asked questions

Why does starter hydration matter for the overall calculation?

Because a sourdough starter itself is made of flour and water in its own ratio, it contributes to both your dough’s total flour and total water — ignoring this and treating the starter as purely additional water produces an inaccurately high hydration calculation.

What’s a typical hydration percentage for sourdough bread?

It varies by desired crumb and crust characteristics, but many sourdough recipes fall roughly in the 65-80% range, with higher hydration doughs generally producing a more open crumb structure and being correspondingly harder to handle during shaping.

How do I adjust a recipe to a different hydration level?

Once you know your total flour weight, calculating the water needed for a target hydration percentage is a matter of multiplying flour weight by the target percentage — accounting for whatever water your starter is already contributing, which is exactly the calculation a hydration calculator handles for you directly.

Final thought

Hydration percentage is a genuinely useful number once it’s calculated correctly, starter included — get the full flour and water totals right, and adjusting or scaling a sourdough recipe to a target hydration becomes straightforward math instead of guesswork.

Try the free Sourdough Hydration Calculator tool