Baker's Percentage Explained: The Only Bread Maths You Need

Baker's percentage looks like a barrier and is actually a shortcut. Once you can read a recipe in percentages you can scale it, compare it to any other recipe, and adjust it without guessing. It takes about five minutes to learn.

The single rule

Flour is always 100%. Everything else is expressed as a percentage of the flour weight.

That's the whole system. It's not a percentage of the total dough, which is why the numbers add up to more than 100 and why that's fine.

A typical loaf:

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

With 500g of flour that becomes 350g water, 100g starter, 10g salt. Multiply each percentage by the flour weight. That's the only calculation in the system.

Why bakers use it instead of cups

It scales instantly. Got 800g of flour left in the bag? 800 × 0.70 = 560g water, 800 × 0.02 = 16g salt. No recipe conversion, no fractions.

It makes recipes comparable. One recipe says 450g flour and 320g water, another says 1kg flour and 780g water. Are they similar? In percentages: 71% and 78%. Very different doughs, obvious instantly.

It tells you what a change will do. Salt at 1.8% versus 2.2% is a meaningful difference in flavour and fermentation speed. In grams it's noise.

The numbers worth memorising

Salt: 1.8–2.2%. Below 1.5% the bread tastes flat and ferments too fast. Above 2.5% it slows fermentation noticeably. Two percent is the default and you can build a whole baking life on it.

Starter: 10–30%. Less starter means slower fermentation and more sour flavour development — good for overnight schedules. More starter means faster, milder bread. Adjust this to fit your day, not the recipe's day.

Water: 65–80% for most sourdough. This is the hydration figure, and it's the one that changes how the dough feels in your hands — our guide to sourdough hydration goes into what each range is like to work with.

The bit that confuses everyone: the starter

Your starter is itself flour and water. So when a recipe says 20% starter, part of that is flour and part is water, and strictly they belong in the totals.

Two approaches:

The simple one, which almost everyone uses: ignore it. Treat starter as its own ingredient at 20% and don't fold it into the flour and water figures. It's slightly imprecise and completely fine for home baking.

The accurate one: a 1:1:1 starter is half flour, half water. So 100g of starter contributes 50g flour and 50g water. Add those to your totals before calculating. This is "total formula" hydration, and it's why your dough sometimes feels wetter than the stated percentage — the real figure is a couple of points higher.

Use the simple version until something isn't adding up. Then use the accurate one.

Working backwards from a finished loaf

Say you want a 900g loaf and your recipe is 100/70/20/2. Add the percentages: 192. So flour = 900 ÷ 1.92 = about 469g. Round to 470g and calculate from there: 329g water, 94g starter, 9.4g salt.

Allow a little for evaporation during baking — a loaf loses roughly 10–15% of its weight in the oven — so if you want 900g of finished bread, aim for about 1,020g of dough.

Write your formula, not your recipe

The real payoff is that percentages let you keep one formula and vary it deliberately. Your notes stop being "the recipe I found" and become "my loaf, at 72%, 2% salt, 15% starter, 9 hours at 21°C" — which is reproducible and adjustable in a way a copied recipe never is.

Keeping that record in one place is the whole argument for a baking notebook, and what to write in a baking journal covers what's worth logging.

Questions we get asked

Why do baker's percentages add up to more than 100?

Because they're all relative to the flour, not to the total dough. Flour is defined as 100%, so a recipe with 70% water and 2% salt totals 172%. That's correct, not an error.

How much salt should I use in sourdough?

Around 2% of the flour weight — 10g for 500g of flour. Below 1.5% the bread tastes flat and ferments too quickly; above 2.5% fermentation slows noticeably.

Do I include the starter's flour and water?

For precision, yes — a 1:1:1 starter is half flour and half water. For everyday baking, treating starter as a single ingredient at 10–30% is accurate enough.

How do I scale a recipe up or down?

Multiply every percentage by the flour weight you want to use. That's it — no ratios to re-derive, no fractions, and it works at any size.