I have written down in my notes that 1 tsp of KM equates to 6.1gm, or 6100 mg. So 1/16 tsp would be about 380 mg.
It might be of interest to someone that KM breaks down to 57% sulfur dioxide, and the rest is something else. :F Testing seems to indicate that on my KM additions, only about 50% of the SO2 is available as free SO2 according to my A/O test kit. I guess that depends on the amount of free SO2 before the addition.