Ratio of vanilla extract to vanilla beans

[cuda6pak]

I have some store bought Watkins pure vanilla extract I'd like to use for a porter I'm kegging tonight. I was wondering what the approximate amount of vanilla extract is to a homemade extract with one bean. 1-2 tsp per vanilla bean?

 

[11oclockBrewery]

I'm not sure about the conversion, but I used 4 whole vanilla beans for a 5gallon batch of Stout and it came out quite well, The vanilla is obvious, probably 3 beans would have sufficed.