How Baker's Percentage Works

Flour is 100%, and everything is measured against it

Baker's percentage looks wrong the first time you see it. A dough is 100% flour, 70% water, 2% salt and 1% yeast — which totals 173%.

Nothing is broken. These aren't shares of the dough; they're ratios to the flour. Flour is defined as 100% and every other ingredient is expressed as a percentage of it.

The reason bakeries work this way is that a formula written in percentages scales to any batch without re-deriving anything, and two recipes can be compared directly even when one makes a single loaf and the other makes forty.

Enter your flour weight and your percentages:

Your starter is half flour

This is where the arithmetic usually goes wrong, and it's worth being precise about.

A starter at 100% hydration is equal parts flour and water by weight. So 200 g of starter is 100 g of flour and 100 g of water — and both of those are already in your dough before you add anything else.

If you add your full target water on top of that, you've overshot. Here's what it costs, using a 500 g flour dough at a 70% target:

	Starter counted	Starter ignored
Total flour	550 g	500 g assumed
Water added	335 g	385 g
Actual hydration	70%	79.1%

Nine percentage points. That's the difference between a dough you can shape and one that spreads, and it gets blamed on the flour far more often than on the arithmetic.

The Hydration if you ignored the starter's water output exists to show you the size of that gap. With no starter it just matches your target, because then there's nothing to get wrong.

Total flour is what everything is calculated on

Once the starter's flour joins the total, Salt and Yeast follow it. That's the usual convention and it's the one that keeps seasoning consistent when you change how much starter you use.

If your recipe states salt as a percentage of only the flour you scoop from the bag, its figure will read slightly lower than this tool's. Neither is wrong — they're measured against different denominators, so it's worth knowing which one your recipe means.

The percentages are yours, not the tool's

The defaults are ordinary starting points, not an optimum this calculator is claiming.

Bread is far too varied for that. A stiff bagel dough and a ciabatta are both correct at hydrations nowhere near each other. Salt slows fermentation as well as seasoning, so the right figure moves with how long you intend to ferment and at what temperature.

Use your own recipe's numbers. The tool does the arithmetic; the judgement stays with you.

A poolish or biga works the same way

The starter fields aren't sourdough-specific. Any preferment is just flour and water sitting somewhere else:

• A poolish is typically 100% hydration — leave the starter hydration at 100.
• A biga is stiffer, usually somewhere near 50–60% — set it there and the flour/water split follows.

The arithmetic doesn't care whether the preferment is leavened with commercial yeast or a sourdough culture. It only cares how much flour and how much water are inside it.

When the water goes blank

If Water to add shows a dash, the starter alone is bringing more water than your target hydration allows. The combination is impossible as entered — you'd need to add a negative amount of water.

The fix is a higher target hydration or less starter. It shows a dash rather than a negative number because there's no such thing as adding minus fifty grams of water, and a negative there would just look like a bug in the tool.

Weigh it

None of this means anything on a measuring cup.

A cup of flour varies by roughly 20% depending on whether it was scooped from the bag or spooned in and levelled. That swing is larger than the difference between two hydrations you'd treat as meaningfully different — so volume measurement destroys the precision baker's percentage exists to give you.

This is the real reason serious bread recipes are written in grams. A cheap digital scale removes more variability from your baking than almost anything else you could buy for the money.

What this won't tell you

How long to prove, at what temperature, and when the dough is actually ready.

Those depend on your flour, your kitchen and your starter's vigour on the day, and the honest answer is to watch the dough rather than the clock. A number here would look authoritative and be wrong in most kitchens — so the tool converts ratios into weights and stops there.