Sourdough Calculator
Free explainer · US$ 0 / KSh 0
Baker’s percentages, with the arithmetic shown
Flour is 100 percent. Everything else is a percentage of the flour. For sourdough, “hydration” can mean two different things unless you say whether the starter’s flour and water are included. This page uses the same maths as our free calculator.
The convention
Baker’s percentages — also called baker’s math — are a way of writing a bread formula so it can be scaled. The total flour is 100%. Water, salt, starter and any extra ingredients are each a percentage of that flour weight, not of the finished dough. 70% hydration on 500 g of flour is 350 g of water if no other flour or water is hiding in a preferment. The percentages can add up to more than 100%, and that is expected.
This is a professional convention, not a secret. It is how formulas are written in bakeries and in many published bread books. We do not claim a trademark on it, and we are not reproducing anyone’s recipe.
Where sourdough trips people up
A starter is itself a mixture of flour and water. If your starter is at 100% hydration, 100 g of starter is 50 g of flour and 50 g of water. Those grams are already in the bowl when you add the starter. If you ignore them, the dough’s true hydration is not the number you typed.
Our calculator, and the worked example below, use total hydration: all the water, including water already in the starter, divided by all the flour, including flour already in the starter. Starter and salt percentages are of the recipe flour you weigh out — the flour in the “flour” line — not of the combined total. That choice is stated on the calculator itself. Other tools sometimes report only “water you pour / flour you weigh,” which is a different, also honest, number. The two will disagree, and both can be consistent with their own definitions.
A worked example (the calculator’s own self-check)
Take 500 g recipe flour, 75% total hydration, 20% starter at 100% starter hydration, and 2% salt. The free calculator’s built-in check expects the following, and you can type the same figures into the calculator to see them:
- Starter weight = 20% of 500 g = 100 g.
- At 100% starter hydration, that 100 g is half flour and half water: 50 g flour and 50 g water already in the starter. (Generally: starter flour = starter ÷ (1 + starter hydration/100).)
- Total flour = 500 + 50 = 550 g.
- Total water wanted for 75% of 550 g = 0.75 × 550 = 412.5 g.
- Water you still have to pour = 412.5 − 50 = 362.5 g.
- Salt = 2% of the 500 g recipe flour = 10 g.
- Total dough = 500 + 362.5 + 100 + 10 = 972.5 g.
If someone instead treated 75% as “pour 375 g of water onto 500 g of flour” and then added 100 g of starter, the true total hydration would be (375+50)/(500+50) ≈ 77.3%, not 75%. That is why we say the definition out loud.
Walk the same arithmetic yourself
The figures update with the same function as the free calculator. If the starter already holds more water than the target hydration allows, the “water to add” goes negative and the target is unreachable.
The Android app
The dough calculator and the starter-feeding calculator are free (US$ 0 / KSh 0) in the Sourdough Calculator Android app, in English and German, offline, in large type. Optional unlock of a starter log and a daily reminder is about US$ 4.99 (about KSh 648; KSh at 129.91 = US$ 1, Central Bank of Kenya, 6 November 2026, illustrative; Google Play sets the charged price). Google Play: coming soon.
Questions
What is a baker’s percentage?
The total flour is 100%. Every other ingredient is written as a percentage of that flour weight.
How do you count hydration?
Total hydration: all water, including water in the starter, divided by all flour, including flour in the starter. Starter and salt percentages are of the recipe flour.
Are you copying a published recipe?
No. The numbers above are a method example (500 g, 75%, 20%, 2%), not a loaf from a book, and they are the same self-check already built into our calculator.