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Sourdough Starter Ratio Calculator

Enter your starter weight and feeding ratio to see exactly how much flour and water to add.

How it is calculated

The ratio is read as seed : flour : water, with the seed always counting as 1 part. You enter the weight of starter you keep (seed) and the flour and water parts. The tool computes flour = seed × flour parts, water = seed × water parts and total = seed + flour + water. Weights come out in whatever unit you typed, usually grams, with two decimals. All three inputs must be greater than zero; a ratio such as 1:0:1 returns no result, and fractional parts like 2.5 are accepted. Because flour and water are entered separately, you can build a stiffer or wetter starter than the usual equal-parts feed. The total tells you how much starter you will have after feeding, before you discard any.

Worked example

You keep 30 g of starter and want a 1:3:2 feed. Flour to add: 30 × 3 = 90.00 g. Water to add: 30 × 2 = 60.00 g. Total starter after feeding: 30 + 90 + 60 = 180.00 g. Since the flour is 90 g and the water 60 g, this starter is about 67% hydration (60 ÷ 90), stiffer than a 1:1:1 feed would be. If you only need 100 g for a bake, discard the surplus before the next feed.

Try this example →

Common mistakes

  • Entering the amount of flour you want to use instead of the weight of the starter you keep. The seed field is the old starter that stays in the jar.
  • Forgetting that the first number in 1:5:5 is the starter itself. At 1:5:5 with 20 g of seed you add 100 g of flour and 100 g of water, not 20 g.
  • Thinking the ratio sets the hydration. Hydration depends on the water to flour parts only, so 1:3:2 is about 67%, while 1:2:2 is 100%.
  • Mixing volume and weight. The ratio works by weight; a spoonful of flour weighs much less than the same spoonful of water.
  • Reading the total as the amount to bake with. It includes the seed you plan to keep, so subtract the portion you retain for the next feed.

About this calculator

A sourdough starter's feeding ratio is expressed as starter : flour : water by weight — a 1:1:1 ratio feeds it with flour and water each equal to the starter's own weight, while a 1:5:5 ratio dilutes it much further, both of which control how quickly the culture ferments and how sour the resulting bread tastes. A tighter ratio like 1:1:1 ferments faster and suits bakers feeding once or twice a day, while a looser ratio like 1:5:5 slows fermentation and works well for less frequent feeding or a milder sour flavor.

Home bakers adjust this ratio deliberately rather than always defaulting to 1:1:1, because the ratio is one of the main levers for controlling both fermentation speed and flavor development — a starter fed too infrequently at a tight ratio can become overly acidic and weaken, while one diluted too much between feeds can starve and lose leavening power.

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