The formula
amount = flour × percentage ÷ 100
Where it comes from
The advantage of the system is that it lets you scale a dough to any quantity without recalculating proportions, and compare recipes at a glance: if one says 70 % hydration and another 65 %, you know instantly which gives the wetter dough without looking at the grams.
How to work it out by hand
- Set the amount of flour, which will be 100 %
- Multiply the flour by each percentage and divide by a hundred
- Add it all up for the total weight of the dough
What is worth knowing
Hydration is the number that changes the result most. Below 60 % the dough is firm and easy to knead, ideal for starting out. Between 65 % and 70 % sits sandwich bread and most home recipes. Above 75 % the dough turns sticky and is no longer kneaded: it is worked with folds, and in return it gives those big irregular holes of rustic bread. Salt is almost always around 2 % and is not worth cutting: beyond the flavour, it controls the fermentation.