Hi bettyR,
Standard natural vanilla extract (which is the strength for home use) has a standard of identity set by the FDA. Here is some reading links that state the FDA standard.
Pure Vanilla Extract - Nielsen-Massey All about Vanilla Extracts and Flavors
Here is a sight that use those standards and variations for home vanilla making. Maceration is the key... long rest.
Homemade Vanilla Extract » TipNut.com
Luc H