Edible help needed

I make edibles, normally using flower purchased from a dispensary. I used the THC % and this calculator to determine how much butter to add.

A friend (who normally only smokes) has requested cookies using the flower he gets directly from a grower. The grower apparently doesn't know the THC content and my friend is very lackadaisical about it, and doesn't want to ask for more information. So I'm stuck making my best guess.

I noticed that this flower had very little smell compared to what I usually get. I wondered if that has anything to do with potency? Is there like an average amount of THC that can use to estimate how much butter to use? Any advice in this situation? TIA.