I found this on Jerrysseramasllc.com: Cocks standing upright, measured from the ground to the comb range from 6 to 10 inches. I thought it was 8 inches or less....guess i was wrong.
I am not sure but i think the average serama height is around 8 ish. My B class rooster is a little shy of 8 & 1/2, one B class hen is 7 & 1/4 and the other 2 hens are 8 inches....the roos' comb alone is almost an inch. Different class also make the difference in height.