Sourdough Calculator

Baker's percentages: everything is weighed against the flour

Sourdough recipes are written in baker's percentages so they scale to any size. Flour is set to 100%, and every other ingredient is a percentage of the flour weight, not of the total dough. Water at 70% means 70 g of water for every 100 g of flour, no matter whether the loaf uses 500 g or 2,000 g of flour.

The three percentages that define a loaf are the starter share, the hydration and the salt. Standard ranges, consistent with the way published artisan recipes are written:

• Starter: 15% to 25% of flour, with 20% the everyday default
• Water: 70% to 78% for most artisan loaves, 65% for beginners who want a stiffer dough
• Salt: 1.8% to 2.2%, with 2% the near universal choice

Because everything is proportional, doubling the loaf means doubling every gram. That is what makes the calculator on this page work: type the flour you have on hand, and the starter, water and salt follow.

Worked example: a 1,000 g flour loaf

Here is the full calculation for a standard country loaf: 1,000 g of flour, 20% starter, 70% water, 2% salt, all percentages of the flour weight:

• Starter: 1,000 x 0.20 = 200 g
• Water to add: 1,000 x 0.70 = 700 g
• Salt: 1,000 x 0.02 = 20 g

The starter itself is roughly half flour and half water, so it is not an inert add-on. A 100% hydration starter contributes 200 / 2 = 100 g of flour and 100 g of water to the dough. That changes the real numbers:

• Total flour: 1,000 + 100 = 1,100 g
• Total water: 700 + 100 = 800 g
• True hydration: 800 / 1,100 = 72.7%, not the 70% on the label
• Total dough: 1,000 + 200 + 700 + 20 = 1,920 g

This is the step most beginner recipes skip, and it matters when you compare two recipes side by side. A 70% loaf made with 20% starter is a wetter dough than a 70% loaf made with 10% starter.

Starter percentage sets the clock

The starter share is a throttle. More starter means more yeast cells in the dough, so bulk fermentation finishes sooner; less starter buys you a long, flavorful, schedule friendly ferment. Typical timings at a 75 degree F kitchen:

Cold kitchens need the higher end and warm kitchens the lower end. The clock is only a guide: bulk is done when the dough has risen 50% to 75% in a straight sided container and looks domed, airy and slightly jiggly. Time estimates come from the way experienced home baking sources describe fermentation at room temperature, and your own dough is the authority.

Hydration: what the water percentage feels like

Hydration decides how the dough handles and how the crumb opens. These are the working bands:

A useful reference point: the same 1,000 g loaf at 75% hydration takes 1,000 x 0.75 = 750 g of water from the mix, and with 20% starter the true hydration climbs to (750 + 100) / 1,100 = 77.3%. Every 5 points of hydration is about 50 g of water on a 1,000 g flour loaf, which is a noticeable change in stickiness.

Remember that flour brand matters too: some bread flours absorb 2 or 3 points more water than all purpose. If a new bag of flour makes the dough feel loose, hold back 20 to 30 g of the water until you see how it behaves.

Folds and the rhythm of bulk fermentation

Mixed sourdough is weak; folded sourdough is strong. Instead of kneading, you build strength with stretch and folds during the first half of bulk. A typical schedule for the 1,000 g loaf:

Salt slows fermentation slightly and tightens the gluten, which is why it goes in with everything else rather than after. Two folds are enough at 65% hydration; wetter doughs benefit from the full four sets. Fold, do not knead: the goal is to stretch the gluten without tearing the gas bubbles the starter has made.

Temperature moves every number on the clock

Fermentation speed roughly doubles for every 15 degrees F of warmth in the bread range. The same dough that bulks in 5 hours at 78 degrees F can take 9 or 10 hours at 65 degrees F. Three practical adjustments:

• Cold kitchen (below 68 degrees F): raise the starter to 25% of the flour, or use warm water around 90 degrees F to land the dough near 76 degrees F.
• Warm kitchen (above 78 degrees F): drop to 15% starter and expect to finish bulk in 3 to 4 hours.
• Overnight plans: cut the starter to 10% of the flour so a 10 to 12 hour bulk fits a workday or a night's sleep.

A cheap instant read thermometer takes the guesswork out: aim for finished dough temperature near 76 to 78 degrees F. Dough temperature is a better predictor of bulk time than room temperature, because the dough is what is fermenting.

Common starter-math mistakes

Most sourdough disappointments trace back to one of five arithmetic slips, and all five are easy to catch:

• Counting the starter as free flour. A 20% starter at 100% hydration contributes 100 g of flour and 100 g of water to a 1,000 g loaf. Ignoring it makes you think you baked a 70% dough when the true hydration was 72.7%, and wetter doughs get judged as failures when the math was misunderstood.
• Scaling recipes by dough weight. If a recipe makes 1,920 g of dough and you want half, do not halve the flour and keep the starter; halve everything: 500 g flour, 100 g starter, 350 g water, 10 g salt. Total dough comes to 960 g.
• Feeding the starter the wrong amount. To end with 200 g of ripe starter you need to feed 100 g of starter with 100 g of flour and 100 g of water, because the feeding triples the mass at peak, not doubles it. Start from less than you think you need and discard the rest.
• Reading percentages off the wrong base. Percentages are of flour, never of total dough. 2% salt on a 1,000 g flour loaf is 20 g; 2% of the whole 1,920 g dough would be 38.4 g, nearly twice as much, and that dough will taste it.
• Trusting the clock over the dough. The 4 to 6 hour bulk window assumes 20% starter and dough around 76 degrees F. A 65 degree F kitchen can double those hours. Watch for a 50% to 75% rise and a domed, jiggly surface instead of watching the wall.

A pocket check that catches most errors: starter plus water plus salt should come to roughly 92% of the flour weight for a standard 20/70/2 recipe, because 20 + 70 + 2 = 92%. If your gram totals do not line up with that share, one of the five mistakes above is hiding in the bowl.

Why grams beat cups for sourdough

Volume measures are the enemy of consistent bread. A cup of flour can weigh anywhere from about 120 g scooped light to 160 g packed in, a 30% swing. On a recipe calling for 4 cups, that is the difference between 480 g and 640 g of flour, which silently turns a 70% dough into something near 55% or 90%.

Weight removes the guesswork because 1,000 g of flour is 1,000 g of flour in every kitchen. For reference, the USDA's FoodData Central database lists standard weights per household measure for flour, water, sugar and salt, and King Arthur Baking publishes a weight chart that most American recipes agree with. A $15 kitchen scale and the calculator on this page will do more for your loaves than any new Dutch oven.

Starter is the ingredient people most often measure by eye, and it is the one that sets your whole schedule. Weigh it: 200 g means 200 g, and the fermentation clock on this page holds.