New to sourdough

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I'm a little confused about hydration when it comes to percentage or how it's measured in any bread, for that matter. can someone explain a bit? thank you.

being considered 100% all the time. So if you have 1000 grams of flour and you have 800 grams of water, that is 80% hydration. It is the same for dough and for starters/levain/whatever you want to call it. 

Total water / Total Flour x 100

You include the starter too. For Example:

 

500g flour

300g water

10g salt

150g starter @ 100% hydration (75g flour + 75g water)

 

So total flour = 575g

total water = 375g

 

Hydration is 375/575 x 100 = 65.22%