Sourdough Hydration Calculator

Enter Calculation

Flour weight (g)

Hydration (%)

Starter (% of flour)

Salt (% of flour)

Starter hydration (%)

Formula

Show calculation steps (1)

1. Water to add

   

   Subtract the water already contained in the starter from the total water requirement.

Results

Water to Add

300

grams (water already in starter subtracted)

Ingredient	Weight (g)
Starter	100
Water to add	300
Salt	10
Total water in dough	350
Total dough weight	860

What is the Sourdough Hydration Calculator?

This tool turns baker's percentages into exact gram weights for your sourdough loaf. In baking, every ingredient is expressed as a percentage of the total flour weight (which is always 100%). Hydration is simply the water weight divided by the flour weight. This calculator works out how much water, starter and salt you need — and, crucially, it subtracts the water already living in your starter so your final dough hits the hydration you actually wanted.

How to use it

Enter your flour weight in grams, your target hydration percentage (typically 65–80% for most breads), your starter as a percentage of flour (often 15–25%), and your salt percentage (usually 2%). Set your starter hydration — a classic 100% starter is equal parts flour and water. The calculator returns the water to add and a full ingredient breakdown.

The formula explained

Total water needed is Flour × Hydration ÷ 100. Your starter weight is Flour × Starter% ÷ 100. Because a 100% hydration starter is half water, that water counts toward your hydration target, so it is subtracted from the water you pour in. The starter's water portion is its weight ÷ (1 + starterHydration/100) × (starterHydration/100).

$$\text{Water} = \text{Flour} \times \frac{\text{Hydration}\%}{100} - \text{Water in Starter}$$

$$W_{total} = F \times \frac{H}{100}$$

$$W_{add} = W_{total} - \frac{S}{1 + \frac{H_s}{100}} \times \frac{H_s}{100}$$

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Half of a 100% hydration starter is water, which must be subtracted from the added water.

Baker's percentages express every ingredient relative to the total flour weight.

Worked example

For 500 g flour at 70% hydration, 20% starter (100% hydration) and 2% salt: total water = \(500 \times 0.70 = 350\) g; starter = 100 g, of which 50 g is water; salt = 10 g. Water to add = \(350 - 50 = \) 300 g. Total dough = \(500 + 350 + 10 = 860\) g.

FAQ

Does this include the flour in my starter? The hydration figure here is based on your main flour weight, the common home-baking convention. For total-formula accuracy, advanced bakers may add the starter flour into the flour total.

What hydration should I use? 65–70% gives an easy-to-handle dough; 75–85% yields a more open, airy crumb but is stickier to work with.

What if water to add shows 0? That means your starter already supplies all the water the recipe needs — reduce starter or raise hydration.