Maybe depends on what it is for? C's only ever taken it for allergic reactions - 26lbs and 3/4 teas but I'd imagine maybe less for something else? Your nurse line can definitely tell you though.
Huh...my pedi's dosage chart says for 28-33lbs the dose is 11/4 tsp (just over 5mL). The 1/2 tsp dose is for 11-17 lbs!!! It doesn't specify for what it's being used (allergic rxn vs. decreasing congestion/secretions). Like lrn said, maybe it's different dosing for different intended uses? I dunno, I guess I'd ask your pedi! ANd apparently I've been ODing my kids! LOL Hey, it works (including, most importantly, the drowsiness factor!), and they're both still alive, so apparently its not necessarily a bad thing!
Re: Benadryl dosage