Formula math
Sourdough Hydration Calculator
A recipe that says 650 g of water is not a 65% dough once the starter is in the bowl — the starter brings its own flour and water with it. Type in your formula and this calculator shows the hydration the dough actually is, reads the whole thing as baker's percentages, and tells you how much water or flour to add when you are aiming at a specific number. Grams or US cups, any starter hydration, nothing leaves your browser.
Your numbers
Your true hydration, baker's percentages and ingredient table will appear here once you add your numbers and press Calculate hydration.
True hydration
–%
- Total flour
- – g
- Total water
- – g
- Dough weight
- – g
- Salt
- –%
| Ingredient | Weight | Baker's % | Approx. volume |
|---|---|---|---|
| Bread flour (added) | – g | –% | – |
| Water (added) | – g | –% | – |
| Sourdough starter | – g | –% | – |
| Salt | – g | –% | – |
| Total flour | – g | 100% | – |
Hitting your target hydration
How the hydration maths works
Baker's percentages are always measured against the total flour, and the starter hides part of that flour. Here is the whole calculation, in the order the calculator runs it:
- Starter flour = starter weight ÷ (1 + starter hydration ÷ 100)
- Starter water = starter weight − starter flour
- Total flour = flour added + starter flour
- Total water = water added + starter water
- True hydration = total water ÷ total flour × 100
- Baker's % = ingredient weight ÷ total flour × 100
The number a recipe prints on the tin — water added ÷ flour added — is thenaive hydration. The calculator shows both so you can see the gap the starter opens up.
Worked example: the sandwich bread formula
The bakehouse's soft sourdough sandwich bread lists 1,000 g bread flour, 650 g warm water, 260 g active starter and 20 g salt. At a 100% starter — the 1:1:1 feed from the starter guide — the starter carries 130 g flour and 130 g water:
| Ingredient | Weight | Baker's % |
|---|---|---|
| Bread flour (added) | 1,000 g | 88.5% |
| Water (added) | 650 g | 57.5% |
| Sourdough starter (100%) | 260 g | 23.0% |
| Salt | 20 g | 1.8% |
| Total flour | 1,130 g | 100% |
So 650 g of water is 57.5% of the flour as written, but the dough in the bowl is69% hydration — 780 g of water against 1,130 g of flour. That is the difference between reading a recipe and knowing what you are mixing. PressLoad the sandwich bread formula to see it in the calculator.
If you bake by cups
Switch the unit control to US cups and type the amounts you scoop; the calculator converts them to grams before doing any maths. The constants it uses are the ones the recipes here assume:
| Ingredient | Conversion | Worth knowing |
|---|---|---|
| Bread flour | 1 US cup ≈ 120 g | Scooped and leveled; a heavy-handed scoop can weigh 150 g. |
| Water | 1 US cup ≈ 236 g | Water is the one ingredient where a cup is close to exact. |
| Starter | 1 US cup ≈ 240 g | Assumes a 100% hydration starter; a stiffer starter packs heavier. |
| Fine salt | 1 tsp ≈ 6 g | Kosher and flaky salt weigh far less per spoon, so weigh if you can. |
Cups are the reason two bakers can follow one recipe and end up with two different doughs. Every number the calculator reports is a gram weight; the cup and spoon column is there for the days the scale stays in the drawer.
What the calculator does not count
- Oil, honey, milk and eggs. Only flour, water, starter and salt go into the maths. The sandwich bread formula also has 55 g avocado oil and 60 g honey — they add weight, and honey carries a little water, but leaving them out keeps the flour-to-water ratio clean.
- The starter's real hydration. The split is derived from the number you type. A starter fed 1:1:1 sits near 100%; one you have been tightening or loosening will be off, and the true hydration moves with it.
- How the dough feels. Flour absorbs differently from bag to bag and season to season. 75% on a thirsty bread flour is a soft dough; 75% on a weak one is a puddle. Treat the number as the plan and your hands as the check.
- Arithmetic is not diagnosis. If the loaf came out flat, dense or gummy, hydration may not be the culprit at all — proofing and gluten development are covered on the pages linked below.
Sourdough hydration questions
- What hydration is sourdough starter?
- A starter fed the guide's 1:1:1 ratio — equal weights of flour and water — is 100% hydration, so half its weight is flour and half is water. Enter whatever your jar actually is: 60% for a stiff levain, 125% for a loose one. The calculator splits the starter's weight into flour and water from that number, so a starter kept differently than the number you type will shift the true hydration.
- Why is my dough wetter than the recipe's hydration says?
- Because the starter carries water the recipe never lists separately. A formula with 650 g of water and 260 g of starter is not 65% — the starter adds another 130 g of water and 130 g of flour, which lands the dough near 69%. That is why the calculator shows both the water-added figure and the true hydration.
- Is higher hydration always better bread?
- No. Hydration changes how a dough handles and how open the crumb bakes up, but past the point your flour can hold, the dough spreads instead of rising. A 65% sandwich loaf and a 78% open-crumb loaf are both correct at their own numbers. If the dough is slack and the loaf still comes out dense, the problem is usually proofing or gluten development rather than the water.
- How much salt should I use?
- Most bread sits between 1.8% and 2.2% of the total flour, which is what the calculator reports as the salt percentage. Note that the percentage is measured against total flour, including the flour the starter brought — so 20 g of salt in a formula with 1,130 g of total flour is 1.8%, not 2% of the 1,000 g you weighed out.
- Does the water in honey, milk or eggs count?
- Not in this calculator. Only flour, water, starter and salt go into the maths. Honey and oil add weight and honey carries a little water, but counting them would make the flour-to-water ratio depend on ingredients that behave very differently in a dough. If you bake mostly with milk or eggs, treat the hydration here as the flour-and-water skeleton of the formula.