Most loaf breads are around 65-75 percent while most pizza doughs are 80-100% percent. Math is not my best subject so I keep this formula handy so I can look at it and just plug in the numbers when adjusting the hydration of doughs. Knowing how to do this will help you when you have issues with your bread baking or changing your recipe to a sourdough recipe.
How to figure the hydration of your dough
Basic Pizza Recipe
303g hard white or hard red wheat flour
1/4 tsp (heaping) yeast 3g
1/4 tsp. (heaping) salt 3g
260g water = .858 x 100 = 86%
Now this recipe is simple, it doesn't have milk, honey, butter, and other items that may effect this number. Most of the time this ratio is good enough since the other ingredients are usually small amounts. If the recipe has large amounts of other ingredients you will need to look up on the internet what the hydration is and adjust accordingly. A good example is milk, it is about 87% water and the rest is milk solids. So is your recipe has 260g of milk instead of water the actual hydration of the milk is 226g (260g x.87) = 226g You will be using the 226g when figuring the hydration of the dough.
Flour milled from North American hard wheat may have a protein content of 11-14%. It will absorb much more water than, say, a French flour with a protein content in the 8-10% range. You will even see variations from one bag of wheat to another when baking. You may have to adjust the hydration of your dough.
If you are working with a flour that has a weaker gluten like Spelt. You may want to reduce the hydration in the dough to get the desired results depending on what you are making for example like pizza.