{
  "id": "sourdough-starter",
  "version": "2291db9222f8",
  "status": "published",
  "name": "Sourdough Starter Calculator",
  "question": "How do I feed my sourdough starter?",
  "summary": "Works out the flour and water to feed a sourdough starter at a ratio such as 1:1:1 or 1:5:5, from the starter you keep or the total you need, with the fed starter’s hydration.",
  "category": "food",
  "subcategory": "baking",
  "url": "https://www.acalculator.org/food/sourdough-starter-calculator",
  "markdown": "https://www.acalculator.org/food/sourdough-starter-calculator.md",
  "kind": "function",
  "method": "For a feeding ratio S:F:W by weight: flour = starter × F ÷ S; water = starter × W ÷ S. From a total T: starter = T × S ÷ (S + F + W). Hydration = (starter water + water) ÷ (starter flour + flour) × 100, where the kept starter holds starter ÷ (1 + h) of flour.",
  "assumptions": [
    "The ratio is by weight. The kept starter is only flour and water, at the hydration you give (100% means equal weights)."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "from": {
        "title": "Start from",
        "description": "The starter you keep and feed, or the total amount of fed starter you need.",
        "type": "string",
        "enum": [
          "keep",
          "total"
        ]
      },
      "k": {
        "title": "Starter kept",
        "description": "The starter you keep in the jar before feeding.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "mass",
        "minimum": 0.000001,
        "maximum": 100
      },
      "t": {
        "title": "Total starter needed",
        "description": "The fed starter you want, for example for a recipe plus some to keep.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "mass",
        "minimum": 0.000001,
        "maximum": 100
      },
      "s": {
        "title": "Starter part (S)",
        "description": "The starter part of the feeding ratio S:F:W.",
        "type": "number",
        "minimum": 0.01,
        "maximum": 1000
      },
      "f": {
        "title": "Flour part (F)",
        "description": "The flour part of the feeding ratio S:F:W.",
        "type": "number",
        "minimum": 0,
        "maximum": 1000
      },
      "w": {
        "title": "Water part (W)",
        "description": "The water part of the feeding ratio S:F:W.",
        "type": "number",
        "minimum": 0,
        "maximum": 1000
      },
      "h": {
        "title": "Starter hydration",
        "description": "The kept starter’s water as a percent of its flour; 100% for equal weights.",
        "type": "number",
        "x-unit": "percent",
        "minimum": 0,
        "maximum": 1000
      }
    }
  },
  "outputs": {
    "flour": {
      "label": "Flour to add",
      "description": "Starter × F ÷ S.",
      "format": "quantity",
      "unit": "g"
    },
    "water": {
      "label": "Water to add",
      "description": "Starter × W ÷ S.",
      "format": "quantity",
      "unit": "g"
    },
    "starter": {
      "label": "Starter to keep",
      "description": "The starter you feed.",
      "format": "quantity",
      "unit": "g"
    },
    "fed": {
      "label": "Fed starter",
      "description": "Starter + flour + water.",
      "format": "quantity",
      "unit": "g"
    },
    "newHydration": {
      "label": "Fed starter hydration (%)",
      "description": "All the water ÷ all the flour × 100, counting the kept starter’s own flour and water.",
      "format": "number"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "from": "keep",
      "k": "50 g",
      "t": "220 g",
      "s": 1,
      "f": 1,
      "w": 1,
      "h": 100
    },
    "outputs": {
      "flour": 0.05,
      "water": 0.05,
      "starter": 0.05,
      "fed": 0.15,
      "newHydration": 100
    },
    "text": "Feed 50 g of starter with 50 g flour and 50 g water."
  },
  "examples": [
    {
      "given": {
        "from": "keep",
        "k": 0.05,
        "s": 1,
        "f": 1,
        "w": 1,
        "h": 100
      },
      "expect": {
        "flour": 0.05,
        "water": 0.05,
        "fed": 0.15,
        "newHydration": 100
      },
      "source": "Wikipedia, Sourdough (a starter is kept alive by regular feedings of flour and water), https://en.wikipedia.org/wiki/Sourdough (retrieved 2026-10-03); Wikipedia, Baker percentage (hydration: water weight as a percent of flour weight), https://en.wikipedia.org/wiki/Baker_percentage (retrieved 2026-10-03); hand calculation in content.mdx: 50 × 1 ÷ 1 = 50 g each"
    },
    {
      "given": {
        "from": "total",
        "t": 0.22,
        "s": 1,
        "f": 5,
        "w": 5,
        "h": 100
      },
      "expect": {
        "starter": 0.02,
        "flour": 0.1,
        "water": 0.1,
        "newHydration": 100
      },
      "source": "Wikipedia, Sourdough (a starter is kept alive by regular feedings of flour and water), https://en.wikipedia.org/wiki/Sourdough (retrieved 2026-10-03); Wikipedia, Baker percentage (hydration: water weight as a percent of flour weight), https://en.wikipedia.org/wiki/Baker_percentage (retrieved 2026-10-03); hand calculation in content.mdx: 220 ÷ 11 = 20 g starter; 100 g flour and water"
    },
    {
      "given": {
        "from": "keep",
        "k": 0.03,
        "s": 1,
        "f": 2,
        "w": 1,
        "h": 100
      },
      "expect": {
        "flour": 0.06,
        "water": 0.03,
        "newHydration": 60
      },
      "source": "Wikipedia, Baker percentage (hydration: water weight as a percent of flour weight), https://en.wikipedia.org/wiki/Baker_percentage (retrieved 2026-10-03); hand calculation in content.mdx: flour 15 + 60 = 75 g, water 15 + 30 = 45 g, 45 ÷ 75 = 60%"
    }
  ],
  "sources": [
    "Wikipedia, Sourdough: a starter is kept active by regular feedings of flour and water. Retrieved 2026-10-03. https://en.wikipedia.org/wiki/Sourdough",
    "Wikipedia, Baker percentage: ingredient weights as a percent of the flour weight; hydration is the water percentage. Retrieved 2026-10-03. https://en.wikipedia.org/wiki/Baker_percentage"
  ],
  "related": [
    "sourdough",
    "pizza-dough",
    "recipe-scaler"
  ],
  "changelog": []
}