Benadryl for dogs..

I know this question always comes up but I searched and can't find what I am looking for. Sadie has been itching a lot lately, can't figure out why. No food change and she has had recent flea treatment. I am guessing some kind of allergies/hotspots. I want to give her Benadryl. What is the milligram dose per pounds of dog. Is it 1/4 tab (which would be 6.25 mg of a 25mg tab) per 10 pounds?? Sadie is about 25 pounds so she would get 1/2 tab if this is correct. Anyone remember?

1-2 mg. per pound up to three times (or was it 2 times?) per day depending on the severity of the allergy. :)
I know everytime this question comes up I have to look it up again. I never remember either. :)

ETA: I think it is twice a day.