Sourdough dough hydration
100 grams of a 100 % starter brings 50 grams of flour and 50 grams of water into your dough. Enter flour, water and starter, and get total flour, total water and the baker's-percentage hydration of the final dough. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Flour weight
- 500
- Water weight
- 350
- Starter weight
- 100
- Starter hydration percent
- 100
- Starter flour weight
- 50
- Starter water weight
- 50
- Total flour weight
- 550
- Total water weight
- 400
Baker's-percentage hydration is the ratio of total water mass to total flour mass in a dough formula, expressed as a percent. Sourdough bakers track it because starter carries both flour and water into the mix, so the final dough hydration is not simply water divided by flour from the recipe card alone. This calculator accepts flour weight, water weight, optional starter weight, and the starter's own hydration, splits the starter into flour and water components, and returns total flour, total water, and hydration percent with a short formula string.
What baker's-percentage hydration means in a sourdough formula
In professional and artisan baking, every ingredient is scaled as a percentage of the total flour weight rather than as a fixed household measure. Hydration is the water line in that system: if the dough contains five hundred grams of flour and three hundred fifty grams of water with no other water sources, hydration is seventy percent. Sourdough complicates the picture because the starter, or levain, is itself a mixture of flour and water that has already been fermented.
Adding one hundred grams of a one-hundred-percent hydration starter contributes fifty grams of flour and fifty grams of water to the final dough. Those contributions must be added to the bulk flour and bulk water before you divide, otherwise you understate total flour, overstate relative water, or both. The calculator implements the standard split: starter flour equals starter weight times one hundred divided by one hundred plus the starter hydration percent; starter water is the remainder of the starter weight.
Total flour is bulk flour plus starter flour; total water is bulk water plus starter water; hydration percent is total water divided by total flour times one hundred. That definition matches bakery textbooks, formula spreadsheets, and the language home bakers use when they say a dough is seventy-five percent hydration after the levain is mixed in.
Where a sourdough hydration calculator earns its keep
Home bakers scaling a favorite country loaf need a quick check that the levain they built still lands near the target hydration after a last-minute flour or water tweak. Bakery production leads convert bench formulas into sheet totals and want a deterministic oracle that treats starter the same way every shift instead of ad-hoc mental math. Teaching kitchens and online courses use the tool to show why a one-hundred-percent starter changes final hydration even when bulk flour and water look fixed on the card.
Failed validation does not consume balance.
What you can do with it
Home sourdough formula checks
Enter bulk flour, water, and levain weight to confirm final baker's-percentage hydration before bulk fermentation.
Bakery production sheets
Scale starter-inclusive doughs for a shift and verify hydration stays on target when batch size or levain build changes.
FAQ
How is sourdough dough hydration calculated?
Hydration percent equals total water mass divided by total flour mass times one hundred. Total flour is bulk flour plus flour from the starter; total water is bulk water plus water from the starter, using the starter's own hydration to split its weight.
What starter hydration should I use?
Use the baker's percentage of your fed starter. One hundred percent means equal flour and water by weight and is the default. Stiffer starters (for example sixty percent) contribute more flour than water per gram of starter.
Why does the starter change my dough hydration?
Because the starter is itself flour and water. If you divide only the water on the card by the flour on the card, you understate total flour, overstate relative water, or both, so the number no longer describes the final dough.
Can I leave the starter out?
Yes. Without a starter the hydration is simply water divided by flour: 500 grams of flour with 350 grams of water and no other water source is seventy percent. The starter is optional and counts as zero when left empty.
Which unit should I weigh everything in?
Use the same mass unit for flour, water and starter, usually grams. Hydration is a ratio, so the unit cancels out, but mixing grams with ounces in one formula gives a wrong result.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/cook/sourdough-hydration-calc \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"flour_weight":500,"water_weight":350}'const res = await fetch("https://api.kit.forhosting.com/cook/sourdough-hydration-calc", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"flour_weight": 500,
"water_weight": 350
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/cook/sourdough-hydration-calc",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"flour_weight": 500,
"water_weight": 350
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/cook/sourdough-hydration-calc", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"flour_weight":500,"water_weight":350}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"flour_weight":500,"water_weight":350}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/cook/sourdough-hydration-calc", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"flour_weight": 500,
"water_weight": 350
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "cook.sourdough_hydration_calc",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Zero flour weight is rejected as invalid_input because division by flour mass would be undefined.
Input contract, response shape, and error behaviour
Example: five hundred grams flour, three hundred fifty grams water, one hundred grams starter at one hundred percent hydration yields fifty grams starter flour, fifty grams starter water, five hundred fifty grams total flour, four hundred grams total water, and hydration of about seventy-two point seven three percent. POST a JSON body with flour_weight and water_weight as required finite numbers in the same mass unit (grams are typical). flour_weight must be strictly greater than zero; a flour weight of zero fails with invalid_input because baker's-percentage hydration divides by flour mass and a zero flour base is not a dough formula. water_weight must be finite and non-negative; zero water is allowed mathematically and returns zero percent hydration. Optional starter_weight defaults to zero when omitted and must be non-negative when present. Optional starter_hydration_percent defaults to one hundred, the common equal-parts fed starter, and must be non-negative. Numeric strings are accepted; missing required fields, non-finite values, and negative masses fail with invalid_input naming the field and are not billed. On success the body echoes flour_weight, water_weight, starter_weight, and starter_hydration_percent; reports starter_flour_weight and starter_water_weight from the split; reports total_flour_weight and total_water_weight; returns hydration_percent rounded to twelve decimal places for stable goldens; and includes a formula string restating the baker's-percentage identity.
Where a sourdough hydration calculator earns its keep
Keep masses in one unit, pin hydration_percent in tests, and you get reproducible dough hydration for notebooks, bakery software, and edge workers without standing up a full bakery ERP of your own.
Integration use cases
Recipe publishing and teaching
Show readers and students how starter flour and water shift dough hydration with the same number in the free widget and the API.
Technical questions
What if I omit the starter?
starter_weight defaults to zero and starter_hydration_percent defaults to one hundred. Hydration then reduces to water_weight divided by flour_weight times one hundred, the classic no-preferment case.
Why is zero flour weight rejected?
Baker's-percentage hydration divides by flour mass. A flour weight of zero is not a valid dough base, so the task fails with invalid_input and is not billed.
What does the sourdough hydration calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.