Sourdough Starter Feeding Calculator
Feeding ratios make it easier to control how much starter you keep, how much flour and water you add, and how much starter you end up with.
This calculator uses the common starter : flour : water format by weight. You can feed an amount you already plan to retain, or start with the final amount you need and let the calculator work backwards.
It also accounts for the hydration of the starter you begin with, so a stiff starter and a 100%-hydration starter are not treated as if they contain the same proportions of flour and water.
Hydration Details
How Sourdough Feeding Ratios Work
A feeding ratio such as:
1:2:2
means:
- 1 part starter
- 2 parts flour
- 2 parts water
All three parts are measured by weight.
If you retain 30 g starter:
- starter = 30 g
- flour = 60 g
- water = 60 g
Final starter:
30 + 60 + 60 = 150 g
A ratio is not a cup or spoon measurement. Flour and water have different densities, so weighing the ingredients gives a much more reliable feed.
1:1:1 vs 1:2:2 vs 1:5:5
A 1:1:1 feed adds the same weight of flour and water as the starter you retain.
For 30 g retained starter:
- 30 g starter
- 30 g flour
- 30 g water
- 90 g final starter
At 1:2:2:
- 30 g starter
- 60 g flour
- 60 g water
- 150 g final starter
At 1:5:5:
- 30 g starter
- 150 g flour
- 150 g water
- 330 g final starter
A larger feed gives the microorganisms more fresh flour relative to the seed starter and will often take longer to reach peak activity.
That does not give us a fixed fermentation time. Starter maturity, room temperature, flour, water temperature and other conditions can all change how quickly it develops.
Starter Hydration Explained
Starter hydration compares the amount of water in a starter with its flour.
A 100%-hydration starter contains equal weights of flour and water.
For example:
100 g starter at 100% hydration
contains approximately:
- 50 g flour
- 50 g water
A 50%-hydration starter is much stiffer.
If the total starter weighs 150 g:
- flour = 100 g
- water = 50 g
The calculator uses the hydration you enter to work out how much flour and water are already present before the new feed is added.
Why Resulting Hydration Can Change
If your starter begins at 100% hydration and you feed equal flour and water, the finished starter remains at 100%.
But a custom feed does not have to use equal flour and water.
Suppose 30 g of 100%-hydration starter is fed at:
1:2:1
The retained starter contains:
- 15 g flour
- 15 g water
The feed adds:
- 60 g flour
- 30 g water
Final flour:
15 + 60 = 75 g
Final water:
15 + 30 = 45 g
Resulting hydration:
45 ÷ 75 × 100 = 60%
So a custom feeding ratio can deliberately create a stiffer or more liquid starter.
Calculate a Target Amount of Starter
Sometimes the important number is not how much starter you already have, but how much ripe starter your recipe needs.
If you want:
250 g starter
at a feed ratio of:
1:2:2
there are five total ratio parts.
Retained starter:
250 × 1/5 = 50 g
Flour:
250 × 2/5 = 100 g
Water:
250 × 2/5 = 100 g
That gives:
250 g final starter
This mode is useful when you want to build roughly the amount needed for a bake without maintaining an unnecessarily large quantity.
Starter Not Retained
If you enter how much starter is currently in your jar, the calculator can also show the amount that is not being retained for the next feed.
For example:
Current starter:
200 g
Starter retained:
30 g
Starter not retained:
170 g
That amount does not automatically need to be thrown away; it may be used in an appropriate discard recipe or handled according to your normal starter routine.
Why the Calculator Does Not Predict Peak Time
Feed ratio affects fermentation speed, but ratio is only one factor.
Temperature is especially important. A warm mature starter can behave very differently from the same ratio in a cool kitchen.
Starter health, flour choice and water temperature matter too.
For that reason, the calculator gives ingredient quantities and hydration—not an exact 'ready in X hours' prediction.
Follow the starter's actual rise, bubbles, aroma and the method used by your recipe.
Worked Example — 30 g Starter at 1:2:2
Retained starter:
30 g
Feed ratio:
1:2:2
Starter hydration:
100%
Scale:
30 ÷ 1 = 30
Flour to add:
30 × 2 = 60 g
Water to add:
30 × 2 = 60 g
Final starter:
30 + 60 + 60 = 150 g
The retained starter itself contains:
- 15 g flour
- 15 g water
Final flour:
15 + 60 = 75 g
Final water:
15 + 60 = 75 g
Resulting hydration:
75 ÷ 75 × 100 = 100%
Frequently Asked Questions
What does a 1:1:1 sourdough feeding ratio mean?
It means equal weights of retained starter, added flour and added water. For example, 30 g starter is fed with 30 g flour and 30 g water.
What does 1:2:2 mean?
It means one part retained starter, two parts flour and two parts water by weight. A 30 g starter therefore receives 60 g flour and 60 g water.
Does a larger feeding ratio slow fermentation?
It often takes longer for a starter to reach peak after a larger feed because there is more fresh flour and water relative to the seed starter. However, temperature, maturity, flour and starter condition also affect timing, so there is no exact timetable based on ratio alone.
What is a 100% hydration starter?
It contains equal weights of flour and water. A 100 g starter at 100% hydration therefore contains about 50 g flour and 50 g water.
How much starter should I keep before feeding?
There is no universal amount. Keep enough for the feeding ratio and final quantity you need. A smaller maintained starter can reduce the amount you do not retain.
Can I use this calculator for a stiff starter?
Yes. Enter the actual starter hydration rather than assuming 100%. The calculator separates the retained starter into its flour and water contributions before calculating the final hydration.
Does flour type change the feeding ratio?
The mathematical ratio does not change, but flour choice can influence how a starter ferments and feels. The calculator therefore uses weights only and does not attempt to predict fermentation performance from flour type.