High,
Potency of peyote depend on a few circumstances...
* Minerals in soil
* oldness
* Time of harvest !!!!!!!!!!
* and maybe some more
About 2-3 years old are very small!!!!! Asuming they contain mescaline I think you need many more then grimoire's suggestion.
If you know the average % mescaline of peyote at harvest time and you know how much mescaline is needed you can figure it out a lot by your self.
San Pedro is a better source because it grows so much quicker. Has more alkoloids too.
Hoped to have helped you,
Peace,
Eric