Sourdough Starter Feeding Calculator
Feeding ratios are written as starter : flour : water, by weight. 1:1:1 means equal parts of each; 1:5:5 means one part starter to five parts flour and five parts water. The higher the ratio, the more food your starter gets, and the longer it takes to peak.
Pick a ratio, say how much starter you want to end up with and set your kitchen temperature. You'll get the exact grams to mix and an estimated window for when your starter should peak.
What to mix
- Starter
- —
- Flour
- —
- Water
- —
- Total
- —
Water ÷ flour. Your starter settles at this hydration after a few feeds.
Estimated time to peak
EstimateA rule-of-thumb estimate, not a reading of your starter. Young, sluggish or very lively starters can be hours off either way.
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How to use it
- 1
Choose a feeding ratio. 1:1:1 is a good everyday default; 1:5:5 or 1:10:10 slows things down for overnight or all-day schedules.
- 2
Enter the total amount of starter you want after feeding (enough for your recipe plus a little to keep), or switch to entering the amount of starter you're keeping.
- 3
Set your kitchen temperature, and switch between °C and °F if you need to.
- 4
Mix the grams shown, mark the level on your jar, and check back inside the estimated peak window.
The math, explained
Add up the ratio parts, then split the total: starter = total × starter parts ÷ (starter + flour + water parts), and the same for flour and water. For 1:2:2 and 150 g in total, 150 ÷ 5 = 30, so you mix 30 g starter, 60 g flour and 60 g water.
If you start from the starter you're keeping, multiply instead: 20 g kept at 1:5:5 needs 100 g of flour and 100 g of water, for 220 g in total.
The peak time is a rule of thumb, not a measurement, and it's the same model the Boulie app starts from. It assumes a healthy, established starter fed 1:1:1 at 22 °C (72 °F) peaks in about 5 hours.
Bigger feeds give the starter more food to work through, so it takes longer to peak. For a 1:n:n feed the base time at 22 °C is base hours = 4 + n: about 5 h at 1:1:1, 6 h at 1:2:2, 9 h at 1:5:5 and 14 h at 1:10:10.
Temperature scales everything. Fermentation roughly doubles in speed for every 9 °C (about 16 °F) warmer and halves for every 9 °C cooler: hours = (4 + n) × 2^((22 − temperature in °C) ÷ 9), kept between 3 and 14 hours. The window shown runs from 80% to 120% of that figure, rounded to the nearest half hour.
Example: a 1:5:5 feed at 20 °C gives 9 h × 2^(2 ÷ 9) ≈ 9 × 1.17 ≈ 10.5 hours, shown as a window of about 8.5–12.5 hours.
Boulie goes beyond a rule of thumb: it logs every feed and rise check, then learns how your own starter behaves in your kitchen.
Frequently asked questions
What is the best feeding ratio for a sourdough starter?
There isn't a single best ratio. 1:1:1 peaks fastest and suits cooler kitchens or baking the same day. 1:2:2 is a flexible daily ratio. 1:5:5 and 1:10:10 give the starter more food and time, which helps with overnight schedules, hot weather and overly sour starters.
How do I know when my starter has peaked?
At its peak a starter has roughly doubled or more, has a domed, bubbly surface and smells pleasantly tangy. Once the dome flattens or the level starts to drop, it's past peak. A rubber band or marker line at feeding time makes the rise easy to see, or Boulie can read it from a photo.
Why is my starter taking longer to peak than the estimate?
A cool kitchen, cold water, a stiff low-hydration starter, a young starter that isn't fully established or low-protein flour all slow things down. Adding some whole-wheat or rye flour to the feed usually speeds it up. Treat the estimate as a starting point and note what your starter actually does.
How often should I feed my sourdough starter?
At room temperature most starters are fed once or twice a day, ideally around the time they peak. In the fridge, once a week is typical. Feeding at a higher ratio lets you stretch the time between feeds.
Should I discard starter before feeding?
Usually, yes: keep only what you need and feed that. Without discarding, a 1:1:1 feed triples the amount in your jar every time, and you'd need more and more flour to keep the same ratio. Discard isn't wasted, either: it's great in pancakes, crackers and pizza dough.
More sourdough calculators
- Sourdough Hydration Calculator Find your dough's true hydration with the starter's flour and water counted in, plus baker's percentages and a reverse mode for target hydration.
- Levain Build Calculator Build exactly the levain your recipe needs: starter, flour and water in grams from the levain weight or percentage, with a buffer.
- Bulk Fermentation Calculator Estimate how long bulk fermentation will take from your dough temperature and starter percentage, and how much rise to aim for.
- Baker's Percentage Recipe Scaler Convert any bread recipe to baker's percentages and scale it to more loaves, a target dough weight or a simple multiplier.
Keep reading
- The Sourdough Float Test: How to Do It and Why It Fails
How to do the sourdough starter float test, what floating or sinking really means, why it gives false results, and four better ways to check your starter.
- Best Sourdough Starter Apps in 2026: What to Look For
An honest guide to sourdough starter tracker apps: the features that matter, what several popular apps list on the App Store, and where Boulie fits.
- How to Tell When Your Sourdough Starter Is Ready to Bake
Doubling, a domed top, bubbles, smell and timing: how to spot your starter's peak, why the float test misleads, and how temperature changes everything.