Homemade soap and using extracts?

I'm making soaps (Melt and Pour) and I bought 2 extracts to add- Buckthorn and Oat. But I can't figure out how much to use per pound of glycerin. Buckthorn says to use up to 15% in products, and oat is up to 10%. How many teaspoons is that? I know this is probably a simple math problem, but math is not my forte. Can someone tell me how to calculate how much to use per pound of base?