How much fresh ginger do I use?

Hey All,
I am making a molasses/ginger porter. I'm not sure how much fresh ginger to use. Any ideas?

Ginger is one of my favorite ingredients to use. It all depends on how much ginger flavor you want in the final product and what other ingredients you are using. I have a honey ginger lager bottled that used 2oz ginger but this flavor is masked by the amount of honey I used. I have a holiday ale that uses 4oz grated ginger but there are other flavors such as orange peel and cinnamon, cinnamon dominates btw. Finally I have a ginger mead that I used 7oz of ginger to really reach a dry ginger flavor of island ginger beers. This is an area you can play with if you know what level of ginger you are trying to reach. All are 5 gall batches but I crave a JuJu ginger flavor so I keep trying... Also ginger takes a while to settle into the beer so give it some time to mellow..

I just brewed a 5 gal. batch of a Holiday Spice Ale and the recipe called for 2 tsps only, it's my understanding it doesn't take much and can easily be overdone.