TL;DR
Baker's percentage expresses every ingredient as a percentage of the total flour weight, which always equals 100%. A dough with 1,000g flour, 750g water, and 20g salt is 75% hydration and 2% salt. The catch in sourdough: your starter contains both flour and water, so you have to fold its contents into the totals before your percentages are true. A calculator handles that correction instantly.
i ruined a double batch of country loaves in february because of a starter i wasn't counting. i'd scaled a 68% hydration recipe up from 2 loaves to 6 for a saturday market, tripled everything carefully — and got a slack, sticky mess that spread like pancake batter. the recipe said 68%. my dough was actually pushing 74%, because i'd tripled 450g of 100% hydration starter along with everything else and never once counted the water hiding inside it.
that bake taught me the thing this whole post is about: baker's percentages are simple, but sourdough breaks the simple version. once you learn the starter correction, you can scale any recipe to any batch size, hit any hydration on purpose, and read a stranger's recipe formula at a glance.
let's build it from zero.
What is baker's percentage?
Baker's percentage (also called baker's math or formula percentage) is a way of writing a recipe where every ingredient is expressed as a percentage of the total flour weight, and flour itself is always 100%. Instead of "3 cups flour, 1¼ cups water," a formula reads "flour 100%, water 75%, salt 2%, starter 20%" — which describes the ratios of the dough independent of batch size, so the same formula works for one loaf or forty.
The basic math, with real numbers
The rule is one sentence: divide each ingredient's weight by the flour weight, multiply by 100.
Take a simple dough:
| Ingredient | Weight | Baker's % |
|---|---|---|
| Bread flour | 1,000g | 100% |
| Water | 750g | 75% |
| Salt | 20g | 2% |
Water: 750 ÷ 1,000 = 0.75 → 75% hydration. Salt: 20 ÷ 1,000 = 0.02 → 2%.
Notice the percentages add up to more than 100% (here, 177%). That's normal and correct — they're not shares of a pie, they're ratios to the flour. This trips up almost everyone on day one and matters exactly zero after that.
Two anchors worth memorizing: salt in bread almost always lands at 1.8–2.2%, and most sourdough recipes you'll meet live between 65% and 85% hydration. If you calculate a formula and salt comes out at 5%, you haven't discovered a bold new style — you've made an arithmetic mistake.
Why bakers bother (scaling is the superpower)
percentages earn their keep the first time you scale. say your formula is flour 100%, water 72%, salt 2%, and you want six 900g loaves — 5,400g of dough total.
Add up the formula: 100 + 72 + 2 = 174%, or 1.74. Divide the target dough weight by that: 5,400 ÷ 1.74 = 3,103g flour. Then everything else falls out automatically: water = 3,103 × 0.72 = 2,234g, salt = 3,103 × 0.02 = 62g.
no cups, no "multiply the recipe by 2.7 and hope." this is also why professional formulas are written this way — you can read "80% hydration, 20% whole wheat, 2% salt" and know exactly what that dough will feel like before you touch flour.
The starter problem: where sourdough breaks the easy math
here's the part that ruined my february bake. a sourdough starter is not an ingredient like salt — it's a package of flour and water that has to be unpacked into your totals.
Say you're mixing:
- 900g flour
- 630g water
- 200g starter at 100% hydration (equal parts flour and water — so 100g flour + 100g water)
- 20g salt
The naive hydration calc says 630 ÷ 900 = 70%. But the true totals are:
- Total flour: 900 + 100 = 1,000g
- Total water: 630 + 100 = 730g
- True hydration: 730 ÷ 1,000 = 73%
three points doesn't sound like much, but 70% and 73% are noticeably different doughs — and the more starter your recipe uses, the bigger the drift. a recipe with 30% starter miscounted this way can be off by 5+ points of hydration, which is the difference between a shapeable dough and the puddle i scraped off my counter.
And if your starter isn't 100% hydration — plenty of bakers keep stiff starters at 50–65% — the unpacking math changes again: a 200g starter at 50% hydration is ~133g flour and ~67g water, not 100/100.
Doing it with a calculator (and when to bother)
you can absolutely do the starter correction by hand — it's two additions and a division. the case for a calculator isn't that the math is hard; it's that you do it every bake, at 6am, while tired, and a silent 3-point error compounds across a whole market batch.
the free hydration calculator does the correction automatically: enter your flour, water, starter amount, and starter hydration, and it returns true hydration and the full formula. the same math lives in the CrumbCoach app (iOS / Android) with starter-correction built in — and because the app also does recipe costing, the same formula that gives you 73% hydration also tells you the loaf costs $3.85 to make. if you sell your bread, that second number matters as much as the first. (more on that in how to price your baked goods.)
The contrarian take: stop chasing high hydration
clearly-labeled opinion time. sourdough culture — instagram especially — treats hydration like a skill ladder: 65% is for beginners, 85% is for real bakers, and 95% ciabatta-adjacent slack doughs are enlightenment. i think that's mostly nonsense. hydration is a style choice, not a score. a well-fermented 68% loaf with an even crumb beats a mangled 85% loaf every single time, and most beginners chasing high hydration are learning to fight sticky dough before they've learned to read fermentation — the actually hard skill. master 68–72% until shaping is boring. your percentages should serve the bread you want to make, not a leaderboard.
<!-- BAKER QUOTE NEEDED — find a real baker quote about the moment baker's percentages "clicked," or about starter hydration throwing off a recipe. Good hunting grounds: r/Sourdough (search "baker's percentage starter"), The Perfect Loaf comments, King Arthur community, Fresh Loaf forums. Verify the source URL before publishing. -->[BAKER QUOTE NEEDED]
Reading a full formula like a pro
once percentages click, you can read a whole loaf from four lines. here's a classic country-style formula and what each line tells you:
| Line | What it tells you |
|---|---|
| 90% bread flour / 10% whole wheat | mild flavor, mostly white crumb, a touch of wheat character |
| 75% hydration | open crumb territory; moderately sticky to shape |
| 20% starter (100% hydration) | ~4–6 hour bulk at warm room temp; relaxed schedule |
| 2% salt | standard seasoning and fermentation control |
that's the entire point of the system: four numbers describe the dough completely, at any batch size, in any kitchen. it's the closest thing baking has to sheet music.
Frequently asked questions
What is baker's percentage in simple terms?
Every ingredient is written as a percentage of the flour weight, and flour is always 100%. If a recipe uses 1,000g flour and 750g water, that's 75% hydration. The system describes ratios, so one formula scales to any batch size.
Why do baker's percentages add up to more than 100%?
Because they're ratios to the flour, not shares of a whole. Flour is 100% by definition, and water, salt, and starter are each compared against it — so a complete formula typically totals 170–190%. That's expected, not an error.
Does sourdough starter count toward hydration?
Yes, and skipping it is the most common formula mistake. Starter contains both flour and water, so add its contents to your totals before calculating. A 70% recipe can be a true 73–75% once a 100%-hydration starter is counted.
What hydration should a beginner sourdough baker use?
Start at 65–70%. The dough is firm enough to shape confidently while still producing a good crumb. Push higher only after shaping feels easy — high hydration adds difficulty, not automatic quality.
How much salt should sourdough bread have?
Between 1.8% and 2.2% of total flour weight, with 2% as the standard. Below about 1.5% bread tastes flat and ferments too fast; much above 2.5% fermentation slows noticeably and the loaf turns salty.
crumb coach was built for sourdough bakers who sell what they bake — the app runs your hydration math with starter correction, tracks your starter's feedings, and costs out every recipe so pricing isn't a guess. it's free to try on iOS and Android.