Simple Sourdough Calculator

Baker's math for sourdough

Baker's math, or baker's percentages, measures every ingredient against the flour. Flour is always 100%, so a recipe written in percentages scales to any batch: multiply the flour weight by each percentage and you have the grams.

Sourdough adds one wrinkle: the starter is itself flour and water. The classic baker's percentage ignores what is inside the starter, while total hydration counts it. The calculator shows both, and the checkbox under the hydration slider decides which one the slider sets.

Worked example

The calculator starts from a classic loaf: 500 g of flour, 350 g of water, 100 g of starter, and 10 g of salt, for 960 g of dough at 70% hydration (72.7% counting the starter).

1. Water: 500 g × 70% = 350 g.
2. Starter: 500 g × 20% = 100 g. At 100% hydration it holds 50 g of flour and 50 g of water.
3. Salt: 500 g × 2% = 10 g. Total dough: 960 g.
4. Total hydration: (350 g + 50 g) ÷ (500 g + 50 g) = 72.7%.

Sourdough hydration chart

Hydration is the water in a dough as a percentage of its flour. It changes how the dough feels in your hands and how open the crumb bakes. Most sourdough sits between 65% and 75%. Beginners do well at the lower end; 80% and above is for open-crumb loaves and practiced hands.

The table uses 500 g of white bread flour and a 20% starter at 100% hydration, so you can compare the classic and total figures side by side.

Whole wheat, rye, and freshly milled flours absorb more water, so add 5–10 points of hydration for the same feel. Weak or low-protein flour feels wetter at the same number.

How starter and temperature change bulk fermentation

Bulk fermentation is the rise between mixing and shaping. Its length depends mostly on the dough temperature and on how much starter you use. Warmth speeds up the yeast and bacteria; more starter gives them a head start.

In the model, doubling the starter saves about one doubling time of the culture, around two hours at 24 °C (75 °F), and fermentation runs about half as fast at 18 °C (64 °F) as at 24 °C. That is why a warm summer kitchen suits 10% starter or less, while a cold winter kitchen needs 25% or more.

The target rise shrinks as the dough gets warmer, because warm dough keeps fermenting quickly while you shape and proof it. The table estimates the hours to that target with a typical starter.

• Use an aliquot jar: put a spoonful of dough in a straight-sided jar, mark the level with a rubber band, and read the rise there instead of guessing from the bowl.
• Control the dough temperature with the water temperature: warm water in winter, cool water in summer.
• If bulk ran long last time at the same temperature, set the starter strength to sluggish; if it raced, set it to lively.

Estimates for white flour with 2% salt. Whole grains ferment faster, and more salt slows fermentation down.

Starter feeding ratios and peak times

A feeding ratio such as 1:5:5 means 1 part starter, 5 parts flour, and 5 parts water by weight. The more you dilute the starter, the longer it takes to peak, so the ratio is also a scheduling tool: 1:1:1 for a quick feed on baking day, 1:5:5 or 1:10:10 to feed at night and mix in the morning.

Use the levain at or just before its peak, when it has roughly doubled or tripled, smells pleasantly sour, and has a domed, bubbly top. The levain planner above works out the grams and the feeding time for you.

If your starter peaks much later than this, it is sluggish: keep it somewhere warmer and feed it regularly for a few days before baking.

Why is my sourdough dense? Reading the crumb

The crumb records how fermentation went. The loaf cross-section in the simulator shows the three classic results:

• Under-fermented: a tight, gummy crumb with a dense band at the bottom and a few large tunnels under the crust. The loaf may burst open at the score. Give bulk more time or more warmth next time.
• Well fermented: an even, open crumb with glossy walls, a tall loaf, and a pronounced ear. The holes get bigger as hydration goes up.
• Over-fermented: a flat, wide loaf with small, uniform holes, a pale crust, and a sour, sometimes gummy crumb. Shorten bulk, use less starter, or keep the dough cooler.

Other common causes of a dense loaf

• A weak starter that does not double within about 4–8 hours of a feed at room temperature.
• Too little water for the flour, especially with whole grains.
• Not enough strength: skipped folds or loose shaping let the gas escape.
• Slicing too early: the crumb keeps setting for an hour or more after baking.

A simple sourdough schedule

A typical bake with dough at about 24 °C (75 °F) and an overnight cold proof looks like this, and it is the plan the simulator starts from. Change the times above to fit your day.

1. Morning: feed the starter 1:1:1. At 24 °C it peaks in about 4–5 hours.
2. Around noon: mix flour, water, starter, and salt. Bulk fermentation begins.
3. First 2 hours: four sets of stretch and folds, 30 minutes apart.
4. 4–6 hours after mixing: end bulk when the dough has risen about 50% and looks domed and bubbly, then pre-shape.
5. 20–30 minutes later: final shape, then into a floured banneton.
6. Evening to morning: cold proof in the fridge for 12–16 hours.
7. Next morning: bake straight from the fridge in a preheated Dutch oven, then cool for at least an hour.

Frequently asked questions

How the simulator works, and its limits

Recipe numbers are exact baker's math. Fermentation numbers come from a simple model, not from lab measurements. Temperature sets the speed through a square-root (Ratkowsky) growth curve that is fastest around 31 °C (88 °F) and close to zero at 3 °C (37 °F), which is why a fridge nearly pauses the dough.

The rise follows a logistic curve calibrated to common baker reference points: with a 20% starter at 24 °C (75 °F), dough gains about 50% in 5 hours, doubles in about 7, and peaks at roughly 2.2 times its starting volume before it slumps. Doubling or halving the starter shifts the whole curve by about two hours of fermentation. A fed starter peaks after about 1.3 hours plus two hours for each doubling of its dilution.

The target rise follows the aliquot-jar rule of thumb: about +50% at 24 °C, more in cooler dough, and less in warmer dough. The crumb picture is an illustration driven by hydration and fermentation timing, not a photograph.

Flour type, salt, dough strength, and your particular starter can all move real timings by 30% or more. Use the estimates to plan, then trust the dough: a domed, jiggly surface, bubbles on the sides, and the right rise in the jar.

Last reviewed September 29, 2026.