Sourdough Starter Calculator

Split a target starter amount into retained starter, flour and water for any S:F:W feeding ratio, or convert a starter to a new hydration by adding flour or water.

Interactive calculator · Method SOURDOUGH-STARTER-1.0 · Last reviewed: 2026-11-04

Calculate your scenario

Feeding: one part = target ÷ (starter + flour + water parts); each ingredient = its parts × one part.

Your inputs

Try an example

Calculation

Starter wanted after feeding (feed) (g)

Ratio part: starter (parts)

Ratio part: flour (parts)

Ratio part: water (parts)

Current starter hydration (%)

Current starter weight (convert) (g)

Target hydration (convert) (%)

Default worked example. Edit the inputs to calculate your scenario.

Default worked example

Retained starter 18.2 g

Flour to add 90.9 g

Water to add 90.9 g

Resulting hydration 100%

Total starter 200 g

200 g ÷ 11 parts = 18.18 g per part: 18.2 g starter, 90.9 g flour, 90.9 g water.

How to use the calculator

For a feed, enter how much starter you want afterwards and the starter : flour : water ratio. To change hydration, choose “Convert hydration” and enter the starter weight, its hydration and the target.

What the result means

A 1:5:5 feed for 200 g keeps 18.2 g of starter and adds 90.9 g each of flour and water, staying at 100% hydration.

Formula and units

Feeding: one part = target ÷ (starter + flour + water parts); each ingredient = its parts × one part. Hydration = all water ÷ all flour × 100, where the retained starter contributes weight ÷ (1 + hydration) of flour and the rest as water. Converting: to raise hydration add water = target × starter flour − starter water; to lower it add flour = starter water ÷ target − starter flour.

Worked examples

200 g starter fed 1:5:5: Starter wanted after feeding (feed): 200 g; Ratio part: starter: 1 parts; Ratio part: flour: 5 parts; Ratio part: water: 5 parts; Current starter hydration: 100 %; Current starter weight (convert): 100 g; Target hydration (convert): 75 %; Calculation: feed.
Example result: Retained starter: 18.2 g; Flour to add: 90.9 g; Water to add: 90.9 g; Resulting hydration: 100%; Total starter: 200 g.

100 g of 100% starter converted to 75%: Starter wanted after feeding (feed): 200 g; Ratio part: starter: 1 parts; Ratio part: flour: 5 parts; Ratio part: water: 5 parts; Current starter hydration: 100 %; Current starter weight (convert): 100 g; Target hydration (convert): 75 %; Calculation: convert.
Example result: Retained starter: 100 g; Flour to add: 16.7 g; Water to add: 0 g; Resulting hydration: 75%; Total starter: 116.7 g.

Limitations and common mistakes

Weights and hydration only. It does not predict rise, peak time, sourness, temperature effects or food safety, and it assumes the current hydration you enter is accurate.

Assuming a 1:5:4 feed of a 100% starter gives 80% hydration; the retained starter’s own water and flour count too, so it is 81.82%.

Sources and assumptions

Method SOURDOUGH-STARTER-1.0; last formula review 2026-11-04. Sources and their supported claims. Calculation methodology.