Baker's percentage is the notation that makes bread recipes comparable. Flour is defined as 100 percent, and every other ingredient is a percentage of the flour weight — so a 70 percent hydration dough means 700 grams of water for every kilogram of flour, whatever the batch size.
Why flour is the reference
Flour is the ingredient everything else acts on. Water hydrates it, salt tightens the gluten it forms, and yeast eats the sugars in it. So expressing the others against flour describes what the dough will actually be like.
The consequence is that the percentages add up to more than 100, which looks wrong the first time. A basic loaf is 100 flour plus 70 water plus 2 salt plus 20 starter, which is 192 percent — and the dough weighs 1.92 times the flour.
That also makes scaling trivial. Want 1.5 kilograms of dough rather than 2? Divide by the total percentage and you have your flour weight, then everything else follows.
Hydration is the number that changes everything
At 60 percent the dough is stiff and easy to handle, and the crumb comes out tight and even. Bagels and pretzels live down here. At 70 it is a normal, workable bread dough. At 80 and above it is slack, sticky and has to be handled with wet hands and folds rather than kneading.
Higher hydration gives a more open crumb and a moister loaf, and it is harder to shape. There is no correct number — there is the number that suits the bread you want and the skill you have.
Flour matters too. Strong bread flour absorbs more water than all-purpose, and wholegrain absorbs considerably more. The same 75 percent dough is comfortable in wholemeal and soup in a weak white flour.
Salt at two percent, and why
Two percent of the flour weight is the standard, and it is remarkably consistent across traditions. On a kilogram of flour that is 20 grams, which looks like a lot in the bowl and is correct.
Below about 1.5 percent the bread tastes flat — not under-salted exactly, but bland and somehow incomplete. Above 2.5 percent the salt starts slowing fermentation measurably, because it draws water away from the yeast.
Salt also tightens the gluten network, so a dough mixed without it feels slacker than the same dough with it. Bakers who autolyse often hold the salt back deliberately for that reason.
The starter brings its own flour and water
This is the step most calculators skip. A 100 percent hydration starter is half flour and half water by weight, so 200 grams of starter contributes 100 grams of flour and 100 grams of water to the dough.
If you ignore that and add the full water figure on top, the dough ends up wetter than the recipe says, and the effective hydration is higher than the number you chose.
This calculator subtracts the starter's water from the water you add, and reports the true hydration counting the starter's flour. On a 20 percent levain the difference is a couple of points; on a 40 percent levain it is significant.
Weigh, do not measure
A cup of flour weighs anywhere from 120 to 150 grams depending on whether it was scooped, spooned or sifted. That is a 25 percent spread on the most important ingredient in the recipe.
This is the actual reason the same recipe works one day and not the next, and it is why every serious bread recipe is written in grams. A kitchen scale costs less than the flour you will waste learning without one.
Water is easy — one millilitre weighs one gram — so the same scale does both and there is no reason to own a measuring jug for bread.