I LOVE IT! The kids LOVE it also!
Have students take out a sheet of paper and draw an enormous G using up the whole page. Explain that this is the gallon.
Then have them write four Qs to fill up the gallon(4 quarts in a gallon).
Next, have them fill up each Q with 2 Ps(2 pints in a quart).
Finally, fill up each P with two cs(2 cups in a pint).
If you'd like, you can have them fill up each cup with an 8(8 fluid ounces in a cup).
It's visual and helps all of my students.
Hope this helps!