Our Fresh Yield Guide is a great tool to refer to when deciding how much truffle to use on a dish. You’ll see that even very little - 3 grams - is enough to make an impact. There are 28 grams in an ounce of truffles, so at 3 grams, you’re getting about 9 servings. We typically would recommend 3 grams be on an appetizer sized portion. 

That being said, you can add as much as you’d like. Below are general recommendations:
Appetizer: 3 grams
Main: 5 or 7 grams. We would recommend that 5 grams is a ‘healthy’ portion on a main course, 7 grams being generous. 
The Fresh Yield Guide also compares two styles of adding truffles to a dish: shaved or grated. 

For more information on shaving vs grating, read our post: Shaving VS Grating