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Baker's percentage and hydration: how bread recipes actually scale

Most bread recipes are written for one loaf, in whatever units the author happened to use. That works until you want two loaves, or you have 700 g of flour left in the bag instead of the 500 g the recipe assumes, or you want to compare two recipes that look nothing alike. Baker's percentage is the convention bakers use to make recipes comparable and scalable, and once it clicks it is hard to go back to cup measurements.

The one rule: flour is always 100%

In baker's percentage, every ingredient is expressed as a percentage of the total flour weight, and the flour itself is defined as 100%. A recipe with 1000 g flour, 700 g water, 20 g salt and 200 g starter is written as:

  • Flour: 100%
  • Water: 70%
  • Salt: 2%
  • Starter: 20%

Those percentages add up to more than 100%, which surprises people at first. That is expected: the percentages are not shares of the total dough, they are ratios against flour. The number that matters most, and the one people argue about, is the water percentage — the dough's hydration.

What hydration actually changes

Hydration is water weight divided by flour weight, times 100. A dough with 1000 g flour and 700 g water is at 70% hydration. The percentage is a good predictor of how the dough will behave:

  • Around 60–65% — a stiff dough that holds its shape, kneads easily and stays where you put it. Typical of sandwich loaves and many enriched doughs. The crumb tends to be even and fine. Bagel doughs are stiffer still, usually somewhere in the 50s, which is where that dense chew comes from.
  • Around 68–75% — the range most rustic sourdough recipes live in. The dough is slack enough to need folds rather than heavy kneading, and open enough to give an irregular crumb.
  • Above 80% — a very wet dough that spreads if it is not supported. It can produce a dramatically open crumb, but it is genuinely harder to shape, and it punishes under-developed gluten and over-proofing.

None of these boundaries are laws. Flour matters as much as the number: whole grain and freshly milled flours absorb noticeably more water than white bread flour, so 75% hydration in wholemeal can feel stiffer than 70% in white. A recipe's hydration figure is only directly comparable to another recipe using similar flour.

The part most people get wrong: the starter counts

A sourdough starter is flour and water too, and if you ignore that, your real hydration is not what you think it is. A starter kept at 100% hydration — equal weights of flour and water, the most common convention — is half flour and half water by weight. So 200 g of it contributes 100 g flour and 100 g water to the dough.

Take the recipe above: 1000 g flour, 700 g water, 200 g of 100% starter. The stated hydration is 70%, but the true totals are 1100 g flour and 800 g water, which is 72.7% hydration. That gap is small here, and large in recipes that lean on a big proportion of starter.

This is also why a stiff starter changes the maths. A starter fed at 50% hydration (half as much water as flour) is two-thirds flour, one-third water, so the same 200 g contributes about 133 g flour and 67 g water. Swapping one starter for the other without adjusting will move your dough by several percentage points.

The convention of quoting hydration without the starter is not wrong, it is just a convention — but when a recipe behaves differently than its number suggests, this is usually the reason.

Scaling a recipe without breaking it

Because every ingredient is pinned to flour, scaling is arithmetic rather than guesswork. Two situations come up constantly.

You know how much flour you have. Multiply each percentage by your flour weight. With 700 g of flour at the percentages above: water 490 g, salt 14 g, starter 140 g.

You know how much dough you want. This is the more common case — a tin or a banneton takes a certain weight. Add all the percentages together to get the total as a proportion of flour. For 100 + 70 + 2 + 20, that total is 192%. Then divide the target dough weight by that figure to recover the flour weight. For 900 g of dough: 900 ÷ 1.92 ≈ 469 g flour, and every other ingredient follows from its percentage.

Note that this is dough weight, not the weight of the loaf that comes out. Bread loses moisture in the oven — commonly in the region of 10–15% of the dough weight, more for free-standing hearth loaves with a lot of crust, less in a covered tin — and a little more again as it cools. If you need a particular baked weight, scale the dough up to allow for it, and add a few percent on top for what stays behind on the bowl and your hands.

Salt, and why 2% is the number you keep seeing

Salt is almost always quoted between 1.8% and 2.2% of flour weight. It is not only seasoning: salt tightens the gluten network and slows fermentation, so cutting it substantially changes the dough's timing and handling, not just the flavour. At 1000 g flour, 2% is 20 g — a figure worth weighing rather than estimating, because a teaspoon of coarse salt and a teaspoon of fine salt are quite different weights.

The starter counts here too. Professional practice quotes salt against total flour, including the flour your starter brought with it: those 20 g are 2% of the recipe's 1000 g, but only 1.8% of the true 1100 g.

Why weight, not volume

Baker's percentage only works with weights. A cup of flour can vary by a substantial margin depending on whether the flour was scooped or spooned and how settled it was, and that variation lands directly in your hydration. A kitchen scale that reads in single grams removes the problem, and it is the single change that most improves consistency for people who bake regularly.

Working it out

If you would rather not do the arithmetic by hand, the sourdough calculators on this site cover the three cases above: finding a dough's hydration, scaling a full recipe from either flour weight or target dough weight, and working out starter feeding ratios.

The underlying maths is simple enough to do on paper, though, and knowing where the numbers come from is what lets you judge whether a recipe you found somewhere is going to behave the way its author says it will.