For every 2,25 grams of changa, there is 1 gram of spice.

Breakthrough dose per changa weight = Your usual breakthrough dose x 2,25

So if you break through, say, with 30mg spice, you should smoke

30 x 2,25 = 67,5 mg of your changa mixture.

with changa there's no way of telling precisely how much dmt gets infused to each particle of caapi. With changa, just smoke until you cant functionally hit the pipe/bong again. wether that's 2, 3, or 4 hits.....do it that way and you should break thru