# Calculating Sourdough Bread and Sourdough Starter Hydration

1. Calculate sourdough starter hydration
2. Calculate sourdough starter hydration when you combine two sourdough starters
3. Increase and decrease sourdough starter hydration

## What is Baker’s Percentages?

The quantity of ingredients in a sourdough bread recipe is expressed using baker’s percentages, which states the weight of every ingredient as a percentage of the total weight of flour called for in the sourdough bread formulation.

The total weight of flour always corresponds to 100%, while the percentages of every other ingredients is in relation to it.

From examples 1 and 2 below you can see that no matter what the weight of the flour is, it always corresponds to 100% baker’s percentages. This is an important rule to remember that will help us in calculating our sourdough bread and sourdough starter hydration.

Example 1:

Example 2:

## How to calculate sourdough starter hydration?

### Example 3: What is the sourdough starter’s hydration for a mixture of 70g of flour and 88g of water?

Baker’s Percentage Ratio as follows:

Water Percentage/Flour Percentage = Total Water Weight/Total Flour Weight

By keeping only the water percentage variable on the left side of the equation, and moving every other variable on the right side, we get:

Water Percentage (Hydration) = (Total Water Weight/Total Flour Weight) x Flour Percentage

Now we can substitute all the known quantities from the table into the right side of the equation:

Total Water Weight = 88g

Total Flour Weight = 70g

Flour Percentage = 100%

Water Percentage = (Total Water Weight/Total Flour Weight) x Flour Percentage

Water Percentage = (88g/70g) x 100%

Water Percentage = 126%

Sourdough starter hydration = Water Percentage

Sourdough starter hydration = 126%

### Example 4: What is the amount of water required to achieve a 90% hydration starter with 50g of flour?

Baker’s Percentage Ratio as follows:

Water Percentage/Flour Percentage = Total Water Weight/Total Flour Weight

By keeping only the total water weight variable on the left side of the equation, and moving every other variable on the right side, we get:

Total Water Weight = (Water Percentage/Flour Percentage) x Total Flour Weight

Now we can substitute all the known quantities from the table into the right side of the equation:

Water Percentage = 90%

Flour Percentage = 100%

Total Flour Weight = 50g

Total Water Weight = (Water Percentage/Flour Percentage) x Total Flour Weight

Total Water Weight = (90%/100%) x 50g

Total Water Weight = 45g

## How to calculate sourdough starter hydration when you combine two sourdough starters?

### Example 5: What is the new sourdough starter hydration, when you combine two sourdough starters of a known hydration level?

Sourdough Starter 1:

Sourdough Starter 2:

First, we have to calculate the combined total flour weight, and combined water weight:

Combined Total Flour Weight = Flour Weight of Starter 1 + Flour Weight of Starter 2

Combined Total Flour Weight = 50g + 50g

Combined Total Flour Weight = 100g

Combined Total Water Weight = Water Weight of Starter 1 + Water Weight of Starter 2

Combined Total Water Weight = 40g + 50g

Combined Total Water Weight = 90g

We can draw up a new table for the combined sourdough starter:

Similar to example 3, we can calculate the combined sourdough starter hydration using the baker’s percentage ratio:

Water Percentage/Flour Percentage = Total Water Weight/Total Flour Weight

By keeping only the water percentage variable on the left side of the equation, and moving every other variable on the right side, we get:

Water Percentage (Hydration) = (Total Water Weight/Total Flour Weight) x Flour Percentage

Now we can substitute all the known quantities from the combined sourdough starter table into the right side of the equation:

Total Water Weight = 90g

Total Flour Weight = 100g

Flour Percentage = 100%

Water Percentage = (Total Water Weight/Total Flour Weight) x Flour Percentage

Water Percentage = (90g/100g) x 100%

Water Percentage = 90%

Combined sourdough starter hydration = Water Percentage

Combined sourdough starter hydration = 90%

## How to increase and decrease sourdough starter hydration?

### Example 6: How much water should I add to my sourdough starter to increase its hydration level?

Let’s say we want to increase our old sourdough starter of 80% hydration to 110% hydration, we have to only add water.

Old Sourdough Starter:

New Sourdough Starter:

To calculate much water we need to add to our sourdough starter:

Weight of water to be added = New sourdough starter water weight – Old sourdough starter water weight

Since we already know the old sourdough starter water weight, which is 80g, we only have to calculate the new sourdough starter water weight.

Using the baker’s percentage ratio on our new sourdough starter:

Water Percentage/Flour Percentage = Total Water Weight/Total Flour Weight

By keeping only the total water weight variable on the left side of the equation, and moving every other variable on the right side, we get:

Total Water Weight = (Water Percentage/Flour Percentage) x Total Flour Weight

Now we can substitute all the known quantities from the new sourdough starter table into the right side of the equation:

Water Percentage = 110%

Flour Percentage = 100%

Total Flour Weight = 100g

Total Water Weight = (Water Percentage/Flour Percentage) x Total Flour Weight

Total Water Weight = (110%/100%) x 100g

New sourdough starter water weight = 110g

Going back to the equation to calculate the weight of water to be added:

New sourdough starter water weight = 110g

Old sourdough starter water weight = 80g

Weight of water to be added = New sourdough starter water weight – Old sourdough starter water weight

Weight of water to be added = 110g – 80g

Weight of water to be added = 30g

### Example 7: How much flour should I add to my sourdough starter to decrease its hydration level?

Let’s say we want to decrease our old sourdough starter of 80% hydration to 70% hydration, we have to only add flour.

Old Sourdough Starter:

New Sourdough Starter:

To calculate much flour we need to add to our sourdough starter:

Weight of flour to be added = New sourdough starter flour weight – Old sourdough starter flour weight

Since we already know the old sourdough starter flour weight, which is 100g, we only have to calculate the new sourdough starter flour weight.

Using the baker’s percentage ratio on our new sourdough starter:

Water Percentage/Flour Percentage = Total Water Weight/Total Flour Weight

By keeping only the total flour weight variable on the left side of the equation, and moving every other variable on the right side, we get:

Total Flour Weight = (Flour Percentage/Water Percentage) x Total Water Weight

Now we can substitute all the known quantities from the new sourdough starter table into the right side of the equation:

Flour Percentage = 100%

Water Percentage = 70%

Total Water Weight = 80g

Total Flour Weight = (Flour Percentage/Water Percentage) x Total Water Weight

Total Flour Weight = (100%/70%) x 80g

New sourdough starter flour weight = 114g

Going back to the equation to calculate the weight of flour to be added:

New sourdough starter flour weight = 114g

Old sourdough starter flour weight = 100g

Weight of flour to be added = New sourdough starter flour weight – Old sourdough starter flour weight

Weight of flour to be added = 114g – 100g

Weight of flour to be added = 14g

### Example 8: What is the sourdough bread’s hydration level, given a known weight of flour and water?

We may come across a scenario where we found a sourdough recipe that only state the total weight of flour and water and we would like to calculate its hydration level.

The new flour is the flour that we will add on top of the starter that we will be using, and the new water is water that we will also add on top of the starter to form our final dough.

To calculate the hydration of our sourdough bread, we can use the baker’s percentage ratio:

Water Percentage/Flour Percentage = Total Water Weight/Total Flour Weight

By keeping only the water percentage variable on the left side of the equation, and moving every other variable on the right side, we get:

Water Percentage (Hydration) = (Total Water Weight/Total Flour Weight) x Flour Percentage

To get the total water weight of the dough, we have to sum up the new water’s weight, the starter’s water weight, and the weight of the oil. Oil and milk is a liquid at room temperature, hence it is included in the hydration calculation of our sourdough bread.

Total water weight in dough = New water weight + Starter’s water weight + Oil weight

Total water weight in dough = 600g + 100g + 50

Total water weight in dough = 750g

To get the total weight of flour in the dough, we need to sum up the new flour’s weight and the starter’s flour weight.

Total weight of flour in dough = New Flour weight + Starter’s Flour weight

Total weight of flour in dough = 900g + 100g

Total weight of flour in dough = 1000g

The total dough flour weight always corresponds to 100% baker’s percentage.

Hence the new flour’s weight of 900g is 90% baker’s percentage, and the starter’s flour weight of 100g has 10% baker’s percentage (or 10% innoculation).

In this example the starter’s hydration is 100%, since the starter’s flour weight is the same as the starter’s water weight. Hence the starter’s water baker’s percentage is also 10% which is the same as the starter’s flour baker’s percentage.

Now we can substitute all the known quantities from our calculations above into the right side of the baker’s percentage ratio equation:

Total Water Weight = 750g

Total Flour Weight = 1000g

Flour Percentage = 100%

Water Percentage = (Total Water Weight/Total Flour Weight) x Flour Percentage

Water Percentage = (750g/1000g) x 100%

Water Percentage = 75%

Sourdough bread hydration = Water Percentage

### Example 9: What is the amount of water required to achieve a 80% hydration level sourdough bread?

Let’s say we have decided that we would like to bake an 80% hydration sourdough bread, with total flour in the dough to be 500g, and a 10% sourdough starter innoculation of 100% hydration. We would like to know how much water we should add to the dough to achieve the 75% hydration.

The new flour is the flour that we will add on top of the starter that we will be using, and the new water is water that we will also add on top of the starter to form our final dough.

If we add the new water’s baker’s percentage (65% hydration), the starter’s water’s baker’s percentage (10% hydration), and the oil’s baker’s percentage (5% hydration), we will arrive at the 80% hydration of our sourdough bread.

To calculate the new water weight, we can use the baker’s percentage ratio:

Water Percentage/Flour Percentage = Total Water Weight/Total Flour Weight

By keeping only the total water weight variable on the left side of the equation, and moving every other variable on the right side, we get:

Total Water Weight = (Water Percentage/Flour Percentage) x Total Flour Weight

To get the total water weight of the dough, we have to sum up the new water’s weight, the starter’s water weight, and the weight of the oil. Oil and milk is a liquid at room temperature, hence it is included in the hydration calculation of our sourdough bread.

Total Water Weight = New Water Weight + Starter’s Water Weight + Oil Weight

We can plug this into our baker’s percentage ratio equation:

Total Water Weight = (Water Percentage/Flour Percentage) x Total Flour Weight

New Water Weight + Starter’s Water Weight + Oil Weight = (Water Percentage/Flour Percentage) x Total Flour Weight

New Water Weight = [(Water Percentage/Flour Percentage) x Total Flour Weight] – Starter’s Water Weight – Oil Weight

Remember that the total dough flour weight always corresponds to 100% baker’s percentage.

Now we can substitute all the known quantities from the table above into the right side of the equation:

Water Percentage = 80%

Flour Percentage = 100%

Total Flour Weight = 500g

Starter’s Water Weight = 50g

Oil Weight = 25g

New Water Weight = [(Water Percentage/Flour Percentage) x Total Flour Weight] – Starter’s Water Weight – Oil Weight

New Water Weight = [(80%/100%) x 500g] – 50g – 25g

New Water Weight = [400g] – 50g – 25g

New Water Weight = 325g

Sam

Hey there! I'm Sam, your go-to pal for all things sourdough. I've been baking and kneading for 10 fun-filled years, and I can't wait to share the joy of turning simple ingredients into heavenly sourdough bread with you. Grab your apron and let's dive into this amazing world of sourdough bread together on this blog.