Sourdough Starter Calculator
Work out what to feed a sourdough starter at any ratio — and how much flour and water the levain actually contributes to your dough.
A feeding ratio is written starter : flour : water.
How the sourdough starter calculator works
A feeding ratio is written starter : flour : water. At 1:5:5 you take one part of your existing starter and add five parts each of flour and water, so 20 g of starter becomes 220 g. A bigger ratio means a longer, slower rise because the yeast has further to go, which is why a warm kitchen wants 1:5:5 and a cold one 1:2:2.
The part bakers forget is that a 100% hydration starter is half flour and half water. If a recipe calls for 200 g of levain, that is 100 g of flour and 100 g of water already in your dough — and both must be subtracted from the recipe totals, or the dough comes out wetter than intended.
Formula: fed weight = starter × (1 + flour ratio + water ratio); levain flour = levain ÷ 2 at 100% hydration
Worked examples
| Inputs | Fed starter weight | Note |
|---|---|---|
| 20 g starter at 1:5:5 | 220 | 100 g flour, 100 g water — 220 g fed |
| A small 1:2:2 feed | 150 | 150 g fed — ready in 4–6 hours |
| Building a large levain, 1:10:10 | 315 | 315 g — a slow overnight build |
FAQFrequently asked questions
What does 1:5:5 mean?
One part starter, five parts flour, five parts water by weight. So 20 g of starter takes 100 g of each.
Which ratio should I use?
A smaller ratio like 1:2:2 rises fast and suits a cold kitchen; 1:5:5 or more gives a slower, milder starter and suits a warm one.
Do I subtract the levain from my recipe?
Yes, and it is the commonest sourdough mistake. A 200 g levain at 100% hydration is 100 g flour and 100 g water already in the dough.
What is starter hydration?
The water as a percentage of the flour in the starter itself. 100% is equal weights — a loose, liquid starter. A stiff starter is nearer 50%.
How do I know when it has peaked?
It roughly doubles, domes on top and smells tangy rather than sharply sour. Past the peak it sinks and the dome flattens.
Where these figures come from
- US FDA — Safe Minimum Internal Temperatures — the internal temperatures the roasting calculator targets
- NIST SP 811 — Guide for the Use of the International System of Units — the exact weight and volume conversions used throughout
- Food Standards Australia New Zealand — food safety and labelling standards
Last checked: September 2026. Baking ratios follow standard baker's percentage practice; roasting guidance follows published safe internal temperatures.