I would use a couple of cups for a gallon.

What kind of tea are you making?

I use whatever is in my bin to make non-aerobic tea in a five gallon bucket. That's usually 1-2 pints. That makes a really black-looking soup, and I mix it with more water in a watering can to the color of about dark iced tea and pour it on the soil around my plants. I suppose that I use about a quart of the black soup and a two gallon watering can. You do the math :-). It isn't an exact science.