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Sourdough Starter Calculator

Find the exact gram weights of starter, flour, and water for any feeding ratio and target total weight, whether you use a 1:1:1, 1:2:2, or any other parts-based feed.

Feeding ratio (starter : flour : water)

Result

100 g

A 300 g feed at a 1:1:1 ratio needs 100 g starter, 100 g flour, and 100 g water

Quick Answer

The sourdough starter calculator divides a target total feed weight by the sum of the ratio parts, then multiplies by each part number to get individual ingredient weights. For a 1:2:2 ratio at 500 g total: 5 total parts, 100 g per part, so 100 g starter, 200 g flour, 200 g water. Feeding ratios are by weight, not by volume. The result is shown as a three-segment bar displaying the starter, flour, and water proportions.

How A Sourdough Starter Calculator Works, Step By Step

A sourdough starter calculator translates a feeding ratio (such as 1:2:2 or 1:5:5) and a target total weight into exact gram amounts for starter, flour, and water. A feeding ratio states the relative parts of each ingredient by weight, not by volume and not as a fixed number of grams. Because the parts are relative, you can scale any ratio to any jar or batch size by entering your target total weight and letting the calculator do the division. This tool is distinct from the Sourdough Calculator, which builds a full dough recipe from a target hydration and loaf weight. It is also distinct from the Sourdough Hydration Calculator, which finds the true hydration of an existing dough. This calculator answers one specific question: for my feeding ratio and my target amount, how many grams of each ingredient do I need? The result displays as exact gram weights and as a three-segment bar showing the proportion of starter, flour, and water in the mix.

The Sourdough Starter Feed Ratio Formula Explained

Part weight (g) = Target total weight (g) ÷ Total ratio parts. Individual ingredient weights = Part weight × ratio part number.

  • Part weight (g) = Target total weight (g) ÷ Total ratio parts.
  • Starter weight (g) = Part weight × Starter ratio number.
  • Flour weight (g) = Part weight × Flour ratio number.
  • Water weight (g) = Part weight × Water ratio number.
  • Total ratio parts = Starter part + Flour part + Water part (e.g. 1+2+2 = 5).

Using This Sourdough Starter Calculator: Step By Step

Inputs

  • Target total weight of starter, flour, and water combined after the feed in grams.
  • Starter portion in the ratio (e.g. 1 for 1:2:2).
  • Flour portion in the ratio (e.g. 2 for 1:2:2).
  • Water portion in the ratio (e.g. 2 for 1:2:2).

Steps

  1. Decide how much total fed starter you need and enter that as the target weight.
  2. Enter your chosen ratio. For a standard 1:2:2 feed, enter 1, 2, and 2.
  3. Read the starter, flour, and water weights in grams from the results.
  4. Check the three-segment split bar to confirm the visual proportions look right for your ratio.
  5. Weigh out each ingredient directly; do not measure by volume.

Sourdough Starter Ratio Example With Every Step Shown

1:2:2 ratio, 500 g target total weight

  1. Sum ratio parts: 1 + 2 + 2 = 5 total parts.
  2. Find one part weight: 500 g ÷ 5 = 100 g per part.
  3. Calculate each ingredient: Starter = 100g × 1 = 100g, Flour = 100g × 2 = 200g, Water = 100g × 2 = 200g.

100 g starter + 200 g flour + 200 g water = 500 g total (exact).

When A Sourdough Starter Calculator Gives The Right Answer

Use this calculator whenever you need to scale a feeding ratio to a specific jar size or batch requirement. Common situations: you want exactly 300 g of levain for a recipe and need to know the starting amounts for a 1:5:5 build; you are switching from maintaining 50 g to 200 g of starter and need to scale the ratio; or you are following a recipe that states a ratio but not the gram weights, and you need to convert it for your target amount.

For other math calculations, visit the math calculators hub, and check the glossary for definitions of common technical terms.

Assumptions

  • The ratio is entered as relative parts by weight; the calculator does not accept volume-based measurements.
  • All three ratio parts must be greater than zero; a zero-starter ratio would mean no culture to ferment.
  • Target total weight is the combined post-feed weight; it does not account for any discard before the feed.
  • Water temperature, flour type, and ambient temperature affect fermentation timing but are not inputs to this calculator.

Limitations

  • Does not calculate fermentation timing or peak activity, which depend on temperature, flour type, and starter age.
  • Does not account for discard removed before feeding; enter the target total of what you are making, not including what you discard.
  • Ratio parts must be positive numbers; fractional ratios (such as 0.5:1:1) are entered as decimals and the formula works identically.
  • Does not calculate dough hydration; for that, use the Sourdough Hydration Calculator.

In Practice

The most common mistake when using a feeding ratio for the first time is assuming the numbers represent grams rather than parts. A 1:2:2 ratio does not mean 1 g of starter, 2 g of flour, and 2 g of water. It means one part starter to two parts flour to two parts water, where the size of one part depends on how much total starter you want to end up with. Once you fix the target total weight, the part size is determined, and every ingredient weight follows automatically. The calculator makes this explicit, but understanding the parts-based logic helps you verify the output mentally before you start weighing.

Related Calculators

Sourdough Calculator

Find the water, starter, salt, and total dough weights for a sourdough batch from flour weight and baker's percentages for home baking.

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Sourdough Hydration Calculator

Find your sourdough dough's true total hydration percentage by entering the recipe flour, water, starter weight, and starter hydration, with the starter's own flour and water counted in full.

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Sourdough Starter Calculator: Frequently Asked Questions

What Does a 1:2:2 Feeding Ratio Mean?

A 1:2:2 ratio means 1 part mature starter to 2 parts flour to 2 parts water, all by weight. For every gram of starter, you add 2 grams of flour and 2 grams of water. At 500 g total, that is 100 g starter, 200 g flour, and 200 g water. The ratio describes the proportion of each ingredient, and the calculator scales it to any target total you choose.

How Is This Different From the Sourdough Hydration Calculator?

The Sourdough Starter Calculator finds how many grams of starter, flour, and water you need for a specific feeding ratio. The Sourdough Hydration Calculator finds the true total hydration of a finished dough recipe, accounting for the water and flour already in the starter. Use this calculator to prepare your feed; use the Sourdough Hydration Calculator to check the hydration of the dough that includes it.

Which Feeding Ratio Should I Use?

The right ratio depends on your schedule and how long you want the starter to take to peak. A 1:1:1 ratio (equal parts) peaks faster (4 to 6 hours at 72 degrees Fahrenheit) and suits bakers who want to use the starter the same day. A 1:2:2 ratio peaks in 6 to 8 hours and is a common all-purpose choice. Higher ratios like 1:5:5 extend peak time to 10 to 14 hours, useful for overnight scheduling. King Arthur Baking's sourdough feeding guides provide a detailed chart of ratio-to-peak-time relationships for different temperatures and flour types.

Can I Use a Non-Standard Ratio Like 1:3:4?

Yes. The formula works for any combination of positive ratio numbers. Enter 1, 3, and 4 as the ratio parts, and the calculator divides the target weight by 8 (1+3+4) to find the part weight, then multiplies by 1, 3, and 4 for each ingredient. A 1:3:4 ratio produces a slightly wetter fed starter (the hydration of the feed itself is 4÷3 × 100 = 133 percent) and a lower proportion of starter to fresh food.

Should I Discard Before Feeding?

Most feeding routines remove most of the mature starter before feeding, keeping only a small portion (the "keep" portion) as the inoculation for the next feed. The amount you keep becomes the starter portion in your ratio. This calculator takes the target total of what you are building after the feed, not the total before discard. Decide how much mature starter to keep, use that as your "1 part," enter the target total you want to end up with, and the calculator gives you the flour and water to add.

Sources

Last updated: . Reviewed for accuracy against the formula shown above.