Sourdough Calculator

This works out a whole loaf formula from one number: the total flour you want to bake with. Everything else is expressed as a percentage of that flour, which is what bakers mean by baker’s percentages.

The formulas:

Water = Total Flour × Hydration % Levain = Total Flour × Levain % Salt = Total Flour × Salt %

The thing that trips people up is that flour is always 100%, so the percentages add to more than 100. A 75% hydration dough is not three-quarters water, it is 750 g of water for every 1,000 g of flour.

Where the levain fits in

Your levain is not a separate ingredient sitting outside the recipe. It is already flour and water, and if you ignore that, the loaf ends up wetter than you asked for. At 100% hydration, which is what most people keep, a 100 g levain is 50 g of flour and 50 g of water.

So the calculator counts the levain’s flour and water toward the totals, then tells you what is left to weigh out separately. Ask for 500 g of flour at 75% with a 20% levain and you get 100 g of levain, of which 50 g is flour, so only 450 g of fresh flour goes in the bowl and 325 g of fresh water.

Weigh out the full 500 g and 375 g and then add the levain on top, and you have really made a 550 g flour loaf with 425 g of water in it. That is 77% hydration, not the 75% you asked for. Two points does not sound like much until you are trying to shape it.

Typical starting points:

Salt below about 1.5% gives a flat-tasting loaf and a slack dough, because salt tightens gluten as well as seasoning. Above 2.5% it starts to slow the yeast noticeably.

Worked example:

500 g flour, 75% hydration, 20% levain, 2% salt.

• Water: 500 × 0.75 = 375 g
• Levain: 500 × 0.20 = 100 g (50 g flour + 50 g water inside it)
• Salt: 500 × 0.02 = 10 g
• So into the bowl: 450 g flour, 325 g water, 100 g levain, 10 g salt
• Total dough: 500 + 375 + 10 = 885 g

A note on flour type: whole wheat and rye drink far more than white flour. Swapping a quarter of the white flour for whole wheat and keeping the hydration the same gives a noticeably stiffer dough, so add 5 to 10 percentage points of water when you do.