Really I'm not even sure how much it matters.
Everyone's reaction is different and if you're just starting you might want to begin with a small to very small dose just to gauge your reaction. You can then work your way up from there. Assuming you're continuing to use the same supply, you should have consistent results this way and the actual percentage isn't even that relevant.
That being said, if you're new to this, I would not recommend going for 50 mg right off the bat. People have had full breakthrough experiences with less than half that much.
Just a recommendation.
Yesterday, upon the stair,
I met a man who wasn't there.
He wasn't there again today,
I wish, I wish he'd go away.