How much benadryl (diphenhydramine) can i give my one year old. she weighs 20 lbs?

Benadryl (diphenhydramine) dose: A safe dose for a 20# 1 year old is 6.25mg, which is a half tsp of the children's liquid. This dose can be given up to 4 times a day (every 6 hours). If needed for more than a couple of days, should consult your doc about other options - is fine short term, but should not be a long term medicine without ok of your pediatrician.