There's a couple of ways you can approach this. You can make a small pre-ferment  or levain using about 15-20g of the starter and 40-50g each of flour and water. J Hamelman's book, "Bread" has a more elaborate description of the methodology on this. Then you'd adjust to reach the per centages of your formula.

On the other hand, I've found the 1-2-3 formula to work for me. It's not very scientific or professional. One part starter, two parts water, and three parts flour. Expect to have to adjust the weights for different flour characteristics and the usual variables. This can be an education on the subject of dough hydration because it's not an exact system.

It works for me, I'm learning more skills, and I'm having fun when I bake. My wife thinks the breads are good enough that she's volunteering me to bake for others. That helps me justify buying more flour and equipment.

Hi and welcome to TFL...it's a site with plenty of tricks and recipes...based on my personal experience I would recommend you to use 140/150  grs per 500 grs of flour. Depending on the room temperature and how healthy is your starter  it will take more or less time to rise, here in Quito with 18º it takes about 9 hours...hope I could help you, happy baking! Paolo

I've had success with this:

With a 100% hydration starter, figure out about how much water you want in the eventual dough. Use 1:1:1 ratio (starter, water, flour) to get to a 100% hydration sponge with 100% of the final water in the sponge and allow that to ferment for 3-24 hours. Taste sponge to tell sourness. Then add all additional ingredients (eggs, sugar, salt, oil, etc) and stir, then add flour to either total flour weight or feel of the dough.

Here's what I did for my last bread:

I knew that I wanted 15 oz of water, so the 100% hydration sponge would have 15 oz of water, 15 oz of flour. I used 10 oz of 100% hydration starter (so 5 oz each of water and flour). I added 10 oz of water, created a slurry with the sponge, and added 10 oz of flour. I put it in my proof box at 90 degrees and it was ready in eight hours. I added 5 egg yolks, three egg whites, 4 oz corn oil, 3 tablespoons sugar, 1.5 teaspoons salt, and stirred to combine. I added 12 oz flour to get to rustic dough consistency, and started adding flour to get a sandwich loaf consistency. I wound up with 60 oz of dough. Two free rises, one bench proof, and 195 degrees (center) later, it tastes great. Very complex.

Hi and welcome to this fantastic site. You just have to know how to use it and you will find tons of info.

How much sourdough to use is a bit different if you bake a white bread or a Rye one. I bake only Rye. I use the method of Sullivan no knead bread. I had to adapt his recipe to my whishing to use rye sourdough, I had tried 2 ways

1) I use 2 cups of white bread flour, 1/2 cup wholemeal,1/2 cup rye, 2tsp salt mix all this and add 1/3 cup of sourdough (liquid- refreshed one day before) and 1$1/2 cup of mineral water. I add 1/2 a tsp of dry yeast (i don't believe the sourdough will make it rise properly!)

2) or I use 2 cups of white bread flour, 1 cup of wholemeal, 100 gram sourdough starter ( refresh one day before) , 1 tsp of salt and 1&1/2 cup of water. and of course 1/2 tsp of dry yest.

I love the result.

To bake white bread seem to be easier and there are many ways to do it.

Use the Fresh loaf motor by writing in "search" on the left of their page. For ex. write San Fransisco sourdough Bread and an avalanche of articles will be given to you. Write just sourdough bread, or any thing else you would like to know again it will be an avalanche of articles and links.

Use the site www.aulevain.canalblog.com by Janedo, it's also a mine of knowledge

try the 1.2.3 formula = 1 part sourdough-2 parts water - 3 parts flour - 1tsp salt it's a recipe given by a French lady. she multiply by two and 3. Her basic quantities are  240g sourdough, 480 gr. water, 720 gr flour. www.makanaibio.com

I spent hundreds of hours to read and learn through those comments and articles to finally reach the recipe I'm happy with. I began by looking in Google France for French baguettes which are a hell of a work to do, and lost a lot of time before I registered to the Fresh loaf, I ended with the no-knead method (Sullivan - no knead bread on you tube ) and arrange it for my Rye sourdough. It's so easy and with almost no efforts.

Registered yourself to get everyday email from the fresh loaf,it's fantastic, suck your time but very usuful, some photos are very inspiring. The comments teach you a lot. I'm now completely addicted to read the Freash Loaf and  to make bread by myself.

I hope I helped you not to wander into Google for hours until you find what you really need. For me the fresh loaf is the ultimate one. Read dmsnyder comments and shiao ping and Eric... and many others they are very good. Good luck from an old french Bee, living now downunder in Sydney...

thx all for the info .. i think i have enough to start working with ..

Bee18 why do you use yeast and sourdough ? my whole point of making the sourdough is to avoide the use of yeast , have you tryed the no knead bread with just sourdough ? do you know how much should i use ? i have been baking the no knead bread for some time now and would love to give it a try without yeast .