Sourdough Calculator
Calculate a sourdough bread recipe (flour, water, starter, salt) with the starter's own flour and water split out of the totals, plus a temperature-adjusted fermentation timeline and starter feeding schedule.
Input
Output
| Ingredient | Grams | Ounces | Baker's % |
|---|---|---|---|
| No data yet | |||
| Phase | Duration | Notes |
|---|---|---|
| No data yet | ||
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/sourdough-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"loaves": "1",
"loafWeight": "900",
"hydrationPercent": "75",
"starterPercent": "20",
"starterHydration": "100",
"saltPercent": "2",
"flourType": "bread-flour",
"temperatureC": "24"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `sourdough-calculator` tool (Sourdough Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/sourdough-calculator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Sourdough Calculator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
Also available with
Guides
What does this tool do?
A sourdough starter is itself roughly half flour and half water (or whatever ratio you feed it at), so it can't be bolted onto a normal baker's-percentage recipe as a single extra ingredient the way commercial yeast can — its own flour and water need to come out of your totals, or the "add from the bag" amounts come out wrong. This calculator does that split for you:
- Enter your loaf count/weight, hydration, starter %, starter hydration, and salt %.
- Get the exact flour and water to add from the bag, the ripe starter weight, and the salt — each shown with its baker's percentage.
- See the starter's own flour and water broken out separately, so you can see exactly how much of your "total flour" and "total water" is already sitting in the starter.
- Get a fermentation timeline — starter feeding, autolyse, bulk fermentation, bench rest, final proof, and baking — adjusted for your kitchen's temperature.
Every weight is shown in grams and ounces, and the breakdown/timeline tables are copyable and downloadable as CSV.
How the starter split works
Baker's percentage always treats total flour = 100%, including the flour already inside your starter. So:
- Total flour and total water are derived from your target dough weight, hydration % and salt %.
- The ripe starter's weight is your starter % of that total flour; its own flour and water portions come from the starter's hydration (a 100%-hydration starter is half flour, half water).
- What you actually add from the bag is the total flour/water minus what the starter is already contributing.
This is why a sourdough recipe's "add" amounts are usually a bit less than a non-starter recipe's would be for the same total hydration — some of the water and flour is already mixed into the starter you're adding.
About the fermentation timeline
Sourdough ferments far more slowly in a cold kitchen than a warm one — roughly twice as fast for every 8°C (about 14°F) warmer, a common baker's rule of thumb (not a precise lab measurement, since starter strength and flour type also matter). The timeline scales the starter feed, bulk fermentation and final proof against a 24°C (75°F) reference using that rule, so a 20°C kitchen gets noticeably longer estimates than a 28°C one. Whole wheat, spelt and rye flours get a shorter suggested autolyse since they hydrate and start breaking down faster than white bread flour. Treat every duration as a starting point — go by the dough's appearance (doubled starter, jiggly and domed bulk ferment) over the clock.
How to use it
- Enter the number of loaves and weight per loaf.
- Set your hydration, starter %, starter hydration and salt % — the defaults are a solid all-purpose starting recipe.
- Pick your flour type and kitchen temperature.
- Read the recipe breakdown and fermentation timeline, or copy/download either table.
FAQ
What starter % and hydration should I use?
20–25% starter (relative to total flour) at 100% hydration (equal parts flour and water) is a common, easy-to-maintain default. A lower starter % (10–15%) ferments more slowly and develops more flavor; a higher one (30%+) speeds things up for a same-day bake. A stiffer starter (50–75% hydration) is common for rye-heavy or very sour loaves.
Why is the flour I add less than my total flour?
Because some of your total flour is already inside the starter you're adding — see "How the starter split works" above. The two sub-rows in the breakdown table show exactly how much.
Can I retard (cold-proof) the dough overnight?
Yes — the final proof estimate here assumes room temperature. A fridge retard (around 4°C) slows fermentation dramatically beyond what this timeline models, and typically runs 8–16 hours regardless of the room-temperature figure shown.
Related tools
For a recipe built around commercial yeast instead of a starter, use the Dough Hydration Calculator or convert between yeast types with the Yeast Conversion Calculator. Scaling a whole recipe for a different pan size is the Baking Pan Size Converter.
Everything is calculated in your browser, with no sign-up, no daily use limit and nothing sent to a server.