How to use baker's percentages to scale a recipe
Baker's percentage is the language professional bakers use to write formulas. Every ingredient is expressed as a percentage of the total flour weight — and flour is always 100%. So "75% water" means the water weighs 75% of the flour; "2% salt" means salt is 2% of the flour. Because everything is relative to flour, you can scale the same formula from one loaf to two hundred without ever changing the ratios.
The scaling math (what this tool does)
Say your formula's percentages add up to S (for a basic sourdough that's 100 + 75 + 20 + 2 = 197). To bake N loaves at W grams of dough each:
1. Total dough = N × W
2. Total flour = Total dough × 100 ÷ S
3. Each ingredient = Total flour × (its % ÷ 100)
That's it. The flour is the anchor; everything else follows from its percentage. This is exactly the calculation that goes wrong in a spreadsheet at 2 a.m. when you're trying to triple a recipe by hand.
About hydration (and your starter)
Hydration is total water ÷ total flour. The catch: your sourdough starter is itself flour and water, so it changes your real hydration. This calculator includes the flour and water inside your starter based on the starter hydration you enter (100% means equal parts flour and water — a typical liquid starter). Set it to match how you feed yours.
A worked example
A 900 g boule at 100% flour / 75% water / 20% starter / 2% salt needs about 457 g flour, 343 g water, 91 g starter, and 9 g salt. Want the full walkthrough? Read How to scale a sourdough recipe with baker's percentages.
More free tools: Sourdough Starter & Levain Calculator · Castiron shut down — the best alternatives in 2026 · Try the free DoughPlan planner