How to Scale a Sourdough Recipe With Baker's Percentages

Once you understand the one rule behind baker's math — flour is always 100% — scaling a single loaf to forty becomes simple arithmetic instead of guesswork. Here's the whole system, with real numbers.

What baker's percentage actually means

Baker's percentage is a way of describing a dough relative to its flour. The rule is simple and slightly weird the first time you meet it:

That's why baker's percentages can add up to well over 100% (a typical sourdough lands somewhere around 185–190% total). They're not slices of a pie; they're ratios pinned to the flour. This is the genius of the system: it describes the character of a dough independent of batch size. A 78% hydration loaf is a 78% hydration loaf whether you're making one or one hundred.

Here's a plain example. Suppose a single loaf uses:

• 500 g flour
• 390 g water
• 10 g salt
• 100 g sourdough starter

To convert to baker's percentage, divide each ingredient by the flour weight and multiply by 100:

• Water: 390 ÷ 500 × 100 = 78%
• Salt: 10 ÷ 500 × 100 = 2%
• Starter: 100 ÷ 500 × 100 = 20%

So this is a 78% hydration, 2% salt, 20% starter loaf. Those three numbers now describe the recipe at any size.

How to compute hydration

Hydration is just the water percentage — water weight divided by flour weight. In the example above, hydration is 78%. The higher the number, the wetter and more open the crumb (and the harder it is to handle).

One subtlety that trips people up: your starter contains flour and water too. A 100% hydration starter (equal parts flour and water by weight) is half flour, half water. If you want your true hydration, you fold the starter's flour and water into the totals. For 100 g of 100%-hydration starter, that's 50 g flour and 50 g water added to your running totals before you divide. For most home formulas the difference is small, but it matters once you're scaling for sale and want consistency loaf to loaf.

How to scale up to N loaves

Scaling is where baker's percentage earns its keep. The trick is to work backward from the dough weight per loaf — the amount of dough you put in each banneton. Here's the four-step method.

1. Add up your total percentage. Flour (100) + water (78) + salt (2) + starter (20) = 200%.
2. Find the flour needed for one loaf. Multiply the per-loaf dough weight by (100 ÷ total %). For a 900 g loaf: 900 × (100 ÷ 200) = 450 g flour.
3. Multiply by the number of loaves. For 40 loaves: 450 × 40 = 18,000 g flour (18 kg).
4. Apply each percentage to that total flour. Every other ingredient is just its percentage of 18,000 g.

That's the entire method. Below it is, worked all the way out.

Worked example: a 78% loaf, 900 g each, scaled to 40 loaves

Per loaf we need 450 g flour (from step 2). Across 40 loaves that's 18,000 g of total flour. Now we apply each baker's percentage to 18,000 g:

Check the math: 18,000 + 14,040 + 360 + 3,600 = 36,000 g, which is exactly 40 × 900 g. The totals reconcile, which is your sign the scaling is correct. Need a different size? A 850 g loaf would need 850 × 0.5 = 425 g flour each; everything else flows from there.

Common mistakes

Scaling the dough weight instead of the flour

The most common error is multiplying the dough weight by your percentages directly — e.g. taking 78% of 900 g. That gives 702 g of water in a single 900 g loaf, which is nonsense. Always derive flour first, then apply percentages to flour.

Forgetting the flour and water hiding in your starter

As above: at small scale it's a rounding error, but 3,600 g of starter carries roughly 1,800 g of flour and 1,800 g of water with it. If you don't account for that, your big batch can drift noticeably wetter than your test loaf.

Rounding salt away

Salt is small in grams but big in flavor and fermentation control. Don't round 360 g down to "about a third of a kilo" — weigh it. At 2% it's one of the few numbers your customers will taste if you get it wrong.

Trusting volume measures

Baker's percentage only works by weight. A cup of flour can vary 20% depending on how it's scooped. Use a scale in grams for everything, including water.

A note on starter and levain

"Starter" and "levain" get used loosely, but for planning they're worth separating. Your starter is the mother culture you maintain. A levain is a specific build you make for a particular bake — often a portion of starter refreshed with flour and water the night before. If your formula calls for 20% levain, you typically build slightly more than you need so you always keep some back to feed as your next starter. When you scale to 40 loaves, remember the levain has to be built ahead and scaled too — it's not something you can conjure at mixing time, which is exactly why a time-reversed schedule matters.

Do it once by hand, then automate it

Working an example like this by hand is the best way to actually understand baker's percentage — do it at least once. After that, you shouldn't be redoing arithmetic every weekend.

For a single recipe, our free baker's percentage calculator handles the conversion and scaling instantly — enter your percentages and a target, get grams. And if you're selling, DoughPlan does this across your whole week of orders at once: it scales every formula to the quantity ordered, rolls all the ingredients into one shopping list, and builds the time-reversed schedule (including when to build your levain) so the math is done before you tie your apron. If you came here from the Castiron shutdown, our alternatives guide covers how production planning fits alongside a storefront.