It's important to know what kind of yeast you are using.
Why? Some recipes call for instant yeast, some for active dry yeast.
To convert instant yeast to active dry yeast, multiply by 1.25.
AKA 1 tsp instant yeast (IDY) = 1.25 tsp active dry yeast (ADY)
To convert active dry yeast to instant yeast, multiply by .75.
AKA 1 tsp active dry yeast (ADY) = 3/4 tsp instant yeast (IDY)
I use Red Star Active Dry Yeast (ADY), which I buy in a 2lb sack at discount at Costco. It's very cheap that way ($5-6 for the bag, which will last you FOREVER!); I put some in separate jars: one small job in the fridge, the rest goes in the freezer, where it will keep more at least a year past the expiration date!