Sourdough Starter Calculator
Calculate flour and water feeding ratios for sourdough starter maintenance and recipe use. Enter values for instant results with step-by-step formulas.
Calculator
Adjust values & calculateFlour in final starter: 100.0g
Water in final starter: 100.0g
Formula
Hydration percentage is water weight divided by flour weight times 100. Feeding ratios like 1:5:5 mean 1 part seed starter to 5 parts flour to 5 parts water by weight. The total weight is divided proportionally among these parts.
Last reviewed: December 2025
Worked Examples
Example 1: Build 200g Starter at 100% Hydration (1:5:5)
Example 2: Daily Maintenance Feed (1:3:3)
Background & Theory
The Sourdough Starter Calculator applies the following established principles and formulas. Cooking and food preparation involve a surprisingly rich set of mathematical relationships that govern texture, flavour, nutrition, and safety. Recipe scaling is perhaps the most immediately practical: to adjust a recipe serving 4 to serve 10, every ingredient quantity is multiplied by the ratio 10/4 = 2.5. This works straightforwardly for most ingredients, but leavening agents, salt, and strong spices often need more conservative scaling because their effects are not strictly linear at larger volumes. Baker's percentage is a professional notation system in which every ingredient is expressed as a percentage of total flour weight. If a dough uses 1000 g flour and 650 g water, the hydration is 65%. This system makes formulas portable across batch sizes and allows bakers to adjust hydration, enrichment, or fermentation characteristics with precision. Temperature conversion between Fahrenheit and Celsius (°C = (°F − 32) × 5/9) is essential when following recipes written for a different regional audience. The Maillard reaction, responsible for browning and the development of complex flavour compounds in bread crusts, roasted meats, and caramelised vegetables, occurs most rapidly above approximately 140°C (285°F) and accelerates with temperature. Yeast activity is highly temperature-sensitive: active dry yeast proofs optimally between 38°C and 43°C (100°F–110°F), and temperatures above 60°C are lethal to yeast cells. Volume-to-weight conversions in cooking rely on ingredient density, which varies significantly: a cup of all-purpose flour weighs approximately 120–130 g, while a cup of honey weighs around 340 g. Relying on volume for dense or variable-density ingredients introduces meaningful measurement error. The pH of a batter determines how leavening agents behave: baking soda (sodium bicarbonate) requires an acid such as buttermilk or vinegar to activate, while baking powder contains its own acidic component and works in neutral batters. Nutritional density calculations, expressed as kilocalories per 100 g, allow comparison of foods on a consistent basis, supporting dietary planning and labelling compliance.
History
The history behind the Sourdough Starter Calculator traces back through the following developments. The culinary arts have ancient roots spanning every human civilisation, but the formalisation of cooking as a measurable, teachable discipline emerged gradually over centuries. Ancient Egyptian, Greek, and Roman texts contain references to food preparation, and medieval European monasteries developed sophisticated brewing and baking traditions that implicitly encoded ratios and techniques passed through apprenticeship. The most transformative figure in modern professional cooking was Auguste Escoffier, whose systematisation of classical French cuisine in the late 19th and early 20th centuries created a codified brigade system and a catalogue of standardised preparations that became the foundation of professional culinary training worldwide. His work, particularly Le Guide Culinaire published in 1903, treated cooking as a discipline with repeatable, transmissible formulas rather than purely intuitive craft. Home economics emerged as a formal academic discipline in the 19th century, partly in response to industrialisation and urbanisation. Figures such as Catharine Beecher and later Ellen Richards in the United States worked to apply scientific principles to domestic cooking and nutrition, eventually institutionalising the subject in schools and universities. Standardised recipe development became central to the food industry in the 20th century as mass food manufacturing required consistent, scalable formulas. The USDA introduced its first food pyramid in 1992 as a public health tool to communicate recommended nutritional ratios to a general audience, though the model has been revised multiple times since. MyPlate replaced the pyramid in 2011 with a simpler visual. Molecular gastronomy, pioneered in the 1990s by chefs such as Ferran Adria at elBulli and Heston Blumenthal at The Fat Duck, brought laboratory techniques and rigorous scientific analysis to high-end cooking, exploring the chemistry of gels, foams, emulsifications, and temperature-controlled preparations. Food calorie labelling laws, mandated on packaged foods in the United States since 1990 under the Nutrition Labeling and Education Act, formalised the expectation that consumers would engage with nutritional arithmetic as part of daily food choices.
Frequently Asked Questions
Formula
Hydration % = (Water Weight / Flour Weight) x 100
Hydration percentage is water weight divided by flour weight times 100. Feeding ratios like 1:5:5 mean 1 part seed starter to 5 parts flour to 5 parts water by weight. The total weight is divided proportionally among these parts.
Worked Examples
Example 1: Build 200g Starter at 100% Hydration (1:5:5)
Problem: A bread recipe requires 200g of active starter at 100% hydration. You have 50g of existing starter. How much flour and water do you need?
Solution: Feeding ratio: 1:5:5 (total 11 parts)\nSeed starter: 200 x (1/11) = 18g\nFlour: 200 x (5/11) = 91g\nWater: 200 x (5/11) = 91g\nTotal: 18 + 91 + 91 = 200g\nDiscard: 50 - 18 = 32g\nAt 75F, peak in ~7 hours
Result: Seed: 18g | Flour: 91g | Water: 91g | Discard: 32g | Peak: ~7 hours
Example 2: Daily Maintenance Feed (1:3:3)
Problem: You want to maintain 100g of starter at 100% hydration with a 1:3:3 ratio. How much of each ingredient?
Solution: Feeding ratio: 1:3:3 (total 7 parts)\nSeed starter: 100 x (1/7) = 14g\nFlour: 100 x (3/7) = 43g\nWater: 100 x (3/7) = 43g\nTotal: 14 + 43 + 43 = 100g\nDiscard remaining starter before adding fresh feed.
Result: Seed: 14g | Flour: 43g | Water: 43g | Faster peak due to higher starter ratio
Frequently Asked Questions
What does hydration percentage mean for sourdough starter?
Hydration percentage expresses the ratio of water to flour by weight, calculated as water weight divided by flour weight times 100. A 100 percent hydration starter has equal weights of flour and water, making it a thick pancake-batter consistency that is the most common and easiest to maintain. A 50 percent hydration starter has half the water weight compared to flour, creating a stiff dough ball that ferments more slowly and produces more acetic acid for a sharper tang. A 125 percent hydration starter is thinner and more pourable. The hydration of your starter directly affects the hydration calculation of your final dough, which is why knowing it precisely matters for consistent bread.
How often should I feed my sourdough starter?
Feeding frequency depends on where you store your starter and how often you bake. A starter kept at room temperature around 70 to 75 degrees Fahrenheit needs feeding every 12 to 24 hours to stay healthy and active. In warmer environments above 80 degrees, it may need feeding every 8 to 12 hours. If you bake infrequently, store your starter in the refrigerator and feed it once a week. Before using a refrigerated starter for baking, take it out and give it two to three feedings at room temperature over 24 to 48 hours to reactivate it fully. A well-fed starter should roughly double in size within 4 to 8 hours of feeding.
What is sourdough discard and can I use it?
Sourdough discard is the portion of starter removed before each feeding to keep the total volume manageable. Without discarding, the starter would grow exponentially with each feeding and quickly become unwieldy. However, this discard is perfectly usable and should not be wasted. Unfed discard can be used immediately in pancakes, waffles, crackers, pizza dough, flatbreads, muffins, and many other recipes. It adds a mild tanginess and complexity to baked goods. Discard can be stored in the refrigerator for up to a week, and you can accumulate it from multiple feedings. There are entire cookbooks dedicated to creative uses for sourdough discard.
How do I know when my starter is ready to bake with?
A mature, active starter shows several reliable signs of readiness. The most dependable test is the float test: drop a small spoonful of starter into a glass of water, and if it floats, the starter is full of gas and ready to leaven bread. A ready starter should have doubled or tripled in volume since its last feeding, have a domed top, and show lots of bubbles both on the surface and along the sides of the jar. It should smell pleasantly tangy and yeasty, not sharp or like nail polish remover. The ideal time to use starter is at or just past its peak volume, usually 4 to 8 hours after feeding depending on temperature and ratio.
What flour should I use for feeding my sourdough starter?
All-purpose white flour is the most common and reliable choice for maintaining a sourdough starter because it provides consistent results and is widely available. Whole wheat and rye flours contain more nutrients and wild yeast, which makes them excellent for establishing a new starter or giving a sluggish one a boost. Many bakers use a blend of 50 percent all-purpose and 50 percent whole wheat for daily feedings. Bread flour works well due to its higher protein content. Avoid bleached flour as the bleaching chemicals can inhibit fermentation. Consistency matters more than the specific flour type, so once you find what works, stick with it for predictable behavior.
Why does temperature matter for sourdough starter?
Temperature is the single most important environmental factor affecting fermentation speed and flavor development. Yeast activity roughly doubles for every 15 degree Fahrenheit increase in temperature. At 75 to 80 degrees, a starter reaches peak activity in 4 to 6 hours and produces a balanced, mildly tangy flavor. At cooler temperatures around 65 degrees, fermentation slows significantly, taking 10 to 14 hours but producing more complex flavors with higher acetic acid content. Above 85 degrees, the bacteria dominate over yeast, increasing sourness but potentially weakening rising power. Understanding temperature allows you to control your starter like a precision instrument, timing feedings and baking around your schedule.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy