A 1:2:2 starter feed describes seed starter, fresh flour and fresh water by mass. It does not mean two grams of flour and water regardless of the amount of seed.
The Whatson Sourdough Starter Feeding Calculator uses those parts to calculate additions, then includes the seed’s existing flour and water when reporting final hydration.
Twenty grams of seed sets the scale
Enter a 20 g seed, one seed part, two flour parts and two water parts. With the seed hydration set to 100%, the checked additions are 40 g fresh flour and 40 g fresh water.
The resulting starter mass is 100 g. The seed contributes another 10 g flour and 10 g water, so the final mixture contains 50 g of each and remains at 100% hydration.
The ratio describes masses, not jar markings or spoon counts. Switching the amount of seed changes both additions proportionally.
The seed hydration affects the final result
A 100% seed hydration means equal flour and water masses in the seed under the calculator’s accounting model. That assumption should be changed when your seed has a different hydration.
For example, a 20 g seed at 50% hydration contains approximately 13.333 g flour and 6.667 g water. Giving it the same 40 g flour and 40 g water feed produces a final hydration of 87.5%, not 100%.
This is why the seed cannot be treated as a single unknown extra when you want to track a formula precisely.
The preset buttons choose ratios, not a readiness time
The available ratio presets populate quantity fields. They do not predict how many hours a particular starter takes to rise, whether it is ready for baking or how it responds to the room temperature in your kitchen.
Use your own starter routine and observations for those decisions. This tool only accounts for the feed and its ingredients.
Plan the recipe starter separately
Sourdough Recipe Calculator calculates how much prepared starter belongs in a full formula. Its target prepared starter mass is a different question from how you divide seed, flour and water for a feed.
If you need both a recipe allocation and an amount to retain, account for that retained quantity in your feeding plan. The calculator does not automatically reserve starter for the next batch.
Save the seed hydration alongside the feed ratio. A note of “1:2:2” on its own cannot fully explain the final hydration when the seed itself is not at 100%.