When I make any sort of recipe I use this formula:
For every 1/8 of weed, use 1 stick of butter (NOT MARGARINE) (1/2 cup). For oil it would be the same: For every 1/8 of weed, use a 1/2 cup of oil.
*Keep in mind we are going for FAT content, it's the ONLY way the THC can be extracted from the weed.
You may ask "why so little butter/oil for soooo much weed?". Well friend, in my experiences and pure logic, the less butter/oil you use for this process the more potent it will be. Fortunately, it works SO well, that my last batch of cupcakes I used an 1/8 of super shitty stress my brother just gave to me, with a stick of butter and holey shit was I on my ass! Shocking, I know!
Now, ideally you'll want to use NO LESS THAN AN 1/8, but if you're going for perfection use no less than 1/4 OZ for a single batch of butter or oil. You can use what ever kind of weed you want. Again, ideally you'll want the best so use the best like chronic, or some kush. Anything with fuzzy red, purple, white, or whatever colored hairs. You can use some stress or some really shitty compressed weed. Your choice. Obviously, if you're going to use super shitty weed you'll want to use a little less butter/oil than 1/2 per 1/8. (Just cut a tbsp off)