Free Sourdough Starter calculator
Build your sourdough recipe by baker's percentage — enter your flour, hydration, starter and salt, and get the exact grams of starter, fresh flour, water and salt to weigh out, with the flour and water inside your starter counted in so the dough hits its target hydration, updated live, as you type.
On this page16 sections
| Ingredient | Weight |
|---|---|
| Total flour | 500 g |
| Ripe starter | 100 g |
| Fresh flour to add | 450 g |
| Fresh water to add | 325 g |
| Salt | 10 g |
| Total dough | 885 g |
Already counted inside the starter: 50 g flour and 50 g water. These are subtracted from the fresh flour and water so the dough hits 75% hydration.
Flour and kitchen conditions vary. How accurate is this?
Results are estimates. Consult a professional.
How the sourdough starter calculator works
A sourdough recipe is built in baker's percentages, where every weight is a share of the total flour and the flour itself is always 100%. This calculator takes your total flour, target hydration, starter percentage and salt percentage, then weighs out the starter, the fresh flour, the fresh water and the salt. The number that sets it apart is hydration: it counts the flour and water already inside your starter so the finished dough hits the hydration you asked for.
What the numbers tell you
Two outputs do the work. The starter weight is what you scoop from your jar, ripe and bubbly. The added flour and added water are what you weigh fresh into the bowl — already reduced by what the starter brought — so when everything comes together the dough sits at your target hydration, not above it. Salt is the small, steady figure that almost never changes.
Baker's percentage and hydration explained
Baker's percentage is the language every bread formula speaks. Flour is fixed at 100%, and water, starter and salt are written as a percentage of that flour weight. It lets you scale a loaf up or down without re-deriving the recipe, because the ratios hold at any size.
Hydration is water over flour
Hydration is the total water divided by the total flour, written as a percentage. A 75% hydration dough has 75 grams of water for every 100 grams of flour. Higher hydration gives an open, airy crumb but a slack, sticky dough; lower hydration is firmer and easier to shape. Most artisan loaves land between 65% and 85%.
Starter percentage sets the pace
Starter percentage is the starter weight as a share of total flour — 20% starter means 200 grams of starter for 1,000 grams of flour. More starter ferments the dough faster; less starter means a longer, slower bulk rise. A typical range is 15% to 25%, with lower amounts suited to long overnight fermentations.
King Arthur defines baker's math as a system where each ingredient is expressed as a percentage of the flour weight, with flour always 100% — the precision method professional bakers use.Why the starter's flour and water count
Here is the mistake that turns a planned 70% dough into a sticky 78% mess. Your starter is not a separate ingredient floating on top of the recipe — it is flour and water that already belong in the dough. Ignore that, and you add full fresh water on top of the water the starter brought, and the loaf comes out wetter than the number on the page.
The starter is part of the dough, not an add-on
A 100% hydration starter is equal parts flour and water by weight. Use 100 grams of it and you have quietly added 50 grams of flour and 50 grams of water before you touch the fresh ingredients. The honest move is to subtract both: take the starter's flour off the fresh flour, and its water off the fresh water.
This is the line most online calculators skip. Many maintenance calculators only handle feeding ratios, and several recipe calculators treat the starter as its own line at the bottom of the formula. This one folds the starter back into the flour and water totals, the way King Arthur and The Perfect Loaf describe it.
The Perfect Loaf's beginner sourdough formula builds a levain from ripe starter, flour and water and carries it into the final dough — the same flour-and-water-in-the-levain accounting this calculator automates.A worked example using the sourdough calculator
Mira is baking one boule built on 500 g of total flour. She wants 75% hydration for an open crumb, a 20% starter for an overnight rise, and the usual 2% salt. Her starter is the standard 100% hydration — equal flour and water.
Step 1 — Weigh the starter
Starter is 20% of the flour: 500 × 0.20 = 100 g starter. At 100% hydration that is 50 g flour and 50 g water already in the bowl.
Step 2 — Work out the total water
Total water is 75% of total flour: 500 × 0.75 = 375 g water. That is the figure the finished dough must reach, starter water included.
Step 3 — Subtract the starter, then weigh fresh
Fresh flour: 500 − 50 = 450 g flour. Fresh water: 375 − 50 = 325 g water. The starter's 50 g of each is already accounted for.
Step 4 — Add the salt and total it up
Salt is 2% of flour: 500 × 0.02 = 10 g salt. The finished dough weighs 500 + 375 + 10 = 885 g.
How much starter, water and salt do I need?
If you want a starting point before you reach for the calculator, this table gives common formulas at a 100% hydration starter. Total flour is the flour the recipe is built on, including the flour inside the starter.
| Total flour | Hydration | Starter (20%) | Added flour | Added water | Salt (2%) |
|---|---|---|---|---|---|
| 500 g | 70% | 100 g | 450 g | 300 g | 10 g |
| 500 g | 75% | 100 g | 450 g | 325 g | 10 g |
| 750 g | 75% | 150 g | 675 g | 488 g | 15 g |
| 1000 g | 70% | 200 g | 900 g | 600 g | 20 g |
| 1000 g | 75% | 200 g | 900 g | 650 g | 20 g |
| 1000 g | 80% | 200 g | 900 g | 700 g | 20 g |
Added flour and added water already have the starter's flour and water subtracted (a 100% hydration starter contributes half its weight as each). Salt is 2% of total flour.
How much starter should I use?
Starter percentage controls speed, not flavour, far more than most bakers expect. The standard range is 15% to 25% of total flour. Use less and the dough ferments slowly, which suits a long overnight bulk; use more and it rises faster, which helps in a cool kitchen or when you are short on time.
- 10–15% starter — slow, overnight fermentation; deeper sour flavour and a forgiving schedule.
- 20% starter — the all-purpose default; a manageable same-day-to-overnight bulk rise.
- 25%+ starter — faster rise for cool kitchens or a tighter timeline; watch it closely so it does not over-proof.
Whatever percentage you pick, the starter must be ripe — bubbly, domed and recently fed — or the dough will lag no matter how much you use. The amount sets the clock; the ripeness sets whether the clock runs at all.
What hydration should I choose?
Hydration decides how the dough feels in your hands and how open the crumb turns out. Beginners do best starting lower, where the dough is firm enough to shape with confidence. As your handling improves you can push the water up for a more open, airy interior.
| Hydration | Dough feel | Best for |
|---|---|---|
| 65–70% | Firm, easy to shape | Beginners, sandwich loaves, batards |
| 72–75% | Soft but workable | Everyday boules, the common sweet spot |
| 78–85% | Slack and sticky | Open crumb, experienced handling |
| 85%+ | Very wet, needs technique | Ciabatta, focaccia, high-hydration loaves |
Ranges follow King Arthur and Serious Eats guidance; Andrew Janjigian suggests beginners start near 75% and most artisan formulas sit between 70% and 85%.
Flour matters too. Whole wheat and rye drink more water than white flour, so a 75% whole-grain dough feels stiffer than a 75% white one. If a dough is fighting you, drop the hydration a few points before you blame your shaping.
Starter hydration: 100% versus stiff starters
Most home starters are kept at 100% hydration, fed equal weights of flour and water, which is why this calculator splits the starter cleanly in half. But not every starter is 100%, and the split changes when it isn't.
Stiff and liquid starters
A stiff starter at 50% hydration is two parts flour to one part water. Use 120 grams of it and you have added 80 grams of flour and 40 grams of water — not 60 and 60. A liquid 125% starter tips the other way, carrying more water than flour. The calculator's starter-hydration field handles either, so the flour-and-water subtraction stays correct whatever you keep on the counter.
Common sourdough formula mistakes
Most sticky-dough complaints trace back to a handful of recurring errors, and nearly all of them are arithmetic rather than technique. Fix the formula first and the dough behaves.
- Stacking the starter's water — adding full fresh water on top of a wet starter, pushing a planned 70% dough toward 80%. Subtract the starter's water instead.
- Forgetting the starter's flour — leaving the starter's flour out of the total, so the real hydration is higher than the label says.
- Using an unripe starter — a flat, hungry starter will not raise the dough no matter what the percentages say.
- Skimping on salt — much below 2% gives a slack, bland dough that ferments too fast; 1.8–2.2% is the reliable band.
- Chasing high hydration too soon — jumping to 85% before your shaping is ready, then fighting a puddle. Build up gradually.
Once the recipe is right, you can scale it to any batch size and convert between cups and grams with our baking conversions tool, or switch units mid-recipe with the cooking converter.
Sourdough terms, defined
How accurate is this sourdough calculator?
The baker's-percentage math is exact. Given your total flour, hydration, starter and salt percentages, the starter weight, fresh flour, fresh water and salt are computed to the gram, with the starter's flour and water subtracted precisely. If your inputs are right, the weights are right.
What the calculator cannot weigh is your kitchen. Flour brands absorb water differently, whole grains drink more than white, and room temperature changes how fast the dough ferments — so the same formula can feel slightly wetter or rise slightly faster than the numbers suggest. Treat the weights as a precise starting point, then trust your hands: if the dough is too slack, drop a few points of hydration next time and write down what worked.
Frequently asked questions about the free Sourdough Starter calculator
About this Sourdough Starter calculator
This sourdough calculator runs entirely in your browser. Nothing you type is sent anywhere — the baker's-percentage math, including the levain accounting that subtracts your starter's flour and water, is computed live on your device and never leaves it.
It is part of our collection of free cooking and baking calculators. Browse the full library of calculators for more kitchen and everyday tools.