If you’ve ever followed a bread recipe exactly and ended up with something completely different from the photo, bread hydration is usually where the gap lives. Two loaves can use identical ingredients in identical proportions and come out with totally different textures — because flour absorbs water differently depending on its protein content, age, and how finely it was milled. Understanding hydration gives you the language to understand why, and the tools to fix it.

Hydration is one of the core concepts in baker’s percentage — a system where every ingredient in a recipe is expressed as a percentage of the total flour weight, not the total recipe weight. This makes recipes scalable and comparable across different batch sizes. Hydration is the most important number in that system because water affects gluten development, crumb structure, crust thickness, fermentation speed, and oven spring all at once.

This guide covers what the numbers actually mean, how to calculate hydration for any recipe, and — critically — how to match hydration level to the bread you’re trying to bake. Different breads need different hydrations, and knowing the target range for each style is what separates bakers who understand their dough from those who are just following instructions.

The formula is straightforward: divide the total water weight by the total flour weight, then multiply by 100.

Hydration % = (Water weight ÷ Flour weight) × 100

For example: 375g water ÷ 500g flour × 100 = 75% hydration. That’s all there is to the maths. The skill is in knowing what to include in those totals — and that’s where most beginners make mistakes.

Any liquid that adds water to the dough counts. That includes milk (which is roughly 88% water), eggs (about 74% water), honey (17–20% water), and even sourdough starter, which is itself a mixture of flour and water. For beginner loaves using only water and flour, the calculation is exact. For enriched doughs with eggs, butter, and milk, it gets more nuanced — but for most everyday baking, adding up the liquid ingredients by weight gives you a close enough working number.

Butter, oil, and other fats do not count toward hydration. They coat gluten strands and affect texture, but they don’t contribute water to the dough’s structure.

If your recipe includes sourdough starter, you need to account for the flour and water inside it. A 100% hydration starter (equal weights flour and water) contributes both equally — so 200g of starter adds 100g flour and 100g water to your running totals. Add those to the main recipe’s flour and water before calculating. Skipping this step consistently underestimates hydration by 3–5 percentage points in most sourdough recipes.

Different bread styles are engineered around specific hydration ranges. Use this chart to understand what you’re aiming for before you start, and to diagnose a dough that isn’t behaving the way you expected.

Hydration isn’t just a number — it changes the physical chemistry of every stage of the bread-making process. Understanding what happens at each stage explains why adjusting hydration by even 5 percentage points can produce a noticeably different loaf.

Water activates the proteins in flour — glutenin and gliadin — which combine to form gluten when mixed. Higher hydration doughs develop gluten more readily because there’s more water to facilitate protein bonding. This is why high-hydration doughs can be made with minimal kneading using techniques like stretch-and-fold: the gluten network builds itself over time as long as sufficient water is present. Lower hydration doughs need more mechanical work (kneading) because there’s less water to lubricate protein-to-protein contact.

Yeast and bacteria thrive in wetter environments. A higher hydration dough ferments faster than a stiff one at the same temperature, because the yeast have easier access to the sugars dissolved in the water. This means a 75% hydration dough will overproof faster than a 62% one if you’re not paying attention. In cold retarding (overnight fridge proofing), high-hydration doughs are more forgiving because the cold slows fermentation enough to give you a wide window to work with.

Water turns to steam in the oven, and that steam is what drives oven spring — the dramatic final rise you see in the first 10–15 minutes of baking. High-hydration doughs have more steam to work with, which produces a more dramatic oven spring, a thinner, crispier crust, and more ear development when scored. This is why professional bakers inject steam into their deck ovens and why home bakers bake sourdough inside a Dutch oven — trapping the steam from the dough itself mimics that effect.

The same hydration percentage produces a completely different dough depending on the flour you’re using. This is one of the most important things to understand when adapting recipes across different flour types.

Bread flour (12–14% protein) absorbs more water than all-purpose flour (10–12% protein). A 72% hydration recipe written for bread flour will feel noticeably stiffer if you substitute all-purpose flour without increasing the water. If you’re swapping from bread to all-purpose, add 2–3% more water to compensate.

Wholemeal and whole wheat flours contain the bran, which absorbs significantly more water than white flour. Recipes with 100% wholemeal flour often target 75–85% hydration to achieve the same workable consistency as an all-purpose dough at 65%. The bran also cuts gluten strands, which is why wholemeal loaves are denser — more water helps, but it doesn’t fully offset the structural impact of the bran.

Rye flour is the extreme case. It contains very little gluten-forming protein and absorbs enormous amounts of water — which is why 100% rye recipes can reach 95–100% hydration and still produce a dough that’s more paste than bread dough. Rye is usually baked in a tin mould because the dough can’t hold a freeform shape at these hydrations.