[header] How to determine benadryl dosage for dogs [title] Find how many milligrams are in a pill of benadryl. [step] Different stores will sell benadryl at different concentrations. Read the label to determine how many milligrams of diphenhydramine a single pill of benadryl contains. 
It's common for benadryl tablets to contain 25 mg, but some may contain a higher or lower amount. [substeps] If you need to obtain benadryl, it should be available at any drug store, pharmacy, or supermarket.