Sourdough Starter Calculator
Work out exactly how much flour and water to feed your starter, what to discard, the 1:x:y ratio, and when it should peak at your room temperature — plus a levain build and a readiness score from the feeds you log.
Your starter
Feeding plan
Flour to add
45 g
Water to add
45 g
Total starter after
150 g
Existing flour / water
30 g / 30 g
Discard (jar limit)
none
Closest ratio
1:1:1
Feeds per day
1
Predicted peak
3 h 59 min
Final hydration
100%
The calculation subtracts the flour and water already inside your starter, so topping up 60 g at 100% to 150 g means adding 90 g of fresh material — not 150 g. Temperature model: about 3 h 30 min to peak at 24 °C, scaled with a Q₁₀-style curve and corrected for your logged performance (1× strength).
Ratio options (starter : flour : water)
Starter readiness
No feeds logged yet
Scored from the rise behaviour you log below (0–100).
Log a feeding
| When | °C | Ratio | Peak | Rise |
|---|
Levain build calculator
Build a separate levain for a dough without feeding the mother jar.
1 : 4 : 4 build (seed, flour, water)
- 22 g of your 100% starter (contains 11 g flour + 11 g water)
- 89 g flour
- 89 g water
Yields 200 g of 100% levain (100 g flour + 100 g water) for a 500 g flour dough. Ready in roughly 3 h 59 min at 22 °C.
Peak times are a model, not a promise: flour type, inoculation rate and starter maturity all shift the curve. Use your logged feedings to bring the strength factor in line with reality.
About this tool
Sourdough Starter Calculator works out the flour and water needed to hit an exact starter weight at your hydration, the discard for a fixed jar, the 1:x:y ratio and a temperature-based peak prediction, then scores readiness from the feedings you log. Feed logs are stored in your browser's localStorage and never leave the device; a levain build calculator covers doughs that need a separate build.
- 100% free — no account needed
- Runs in your browser
- Nothing is uploaded
Frequently asked questions
Is Sourdough Starter Calculator really free?
Yes. Sourdough Starter Calculator is completely free on PureBrowser — every feature, with no account, no trial, and no credit card.
Does Sourdough Starter Calculator upload my data?
No. Sourdough Starter Calculator runs entirely inside your browser, so anything you type, paste, or open stays on your own device.
Do I need to sign up or install anything?
Neither. There is no account and nothing to download — open the page and Sourdough Starter Calculator is ready to use on desktop or mobile.
Does Sourdough Starter Calculator work offline?
Once the page has loaded, yes. All of the processing happens locally in your browser, so it keeps working without a connection.
More kitchen & cooking
Cooking Unit Converter
Convert cups, spoons, ml, grams, and ounces with ingredient-specific density.
Recipe Scaling Calculator
Scale any recipe up or down by changing the number of servings. All ingredient amounts adjust proportionally. Supports cups, grams, ml, oz, and more.
Baking Substitutions Guide
Find substitutes for 35+ baking ingredients — eggs, butter, flour, sugar, dairy, and more. Exact ratios, instructions, and best-use tips included.
Pizza Portion & Pan Calculator
Work out how many pizzas to make from the number of guests or the pan size, with real area maths, dough weight per base and a scaled shopping list.
Pizza Dough Calculator
Scale pizza dough by the number of pizzas, ball weight and style — Neapolitan, New York, Detroit and more — with correct pre-ferment mathematics and a fermentation schedule.
Recipe Converter & Formatter
Paste a recipe and convert it properly: scale the servings, parse the ingredient lines, convert cups and ounces to grams using real ingredient densities, and format kitchen fractions.