I'm with auntdot - you have to know the weight of a given volume of something before you can start converting between volume and weight for that something. A teaspoon of water and a teaspoon of dry yeast do not weight the same - and a teaspoon of dry yeast does not weigh the same as a teaspoon of cake fresh yeast.
For dry yeast (like in those little foil packets or in glass jars) - 1 teaspoon of yeast weighs about 3.1 g.
1 packet of dry yeast weighs 1/4 oz or 7 grams, and contains about 2 1/4 teaspoons. So, if my math still works, 7 grams divided by 2.25 teaspoons = 3.11 grams per teaspoon.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain