It's a clear plastic bag, I am not sure how to translate 1 quart to dimensions. I've seen 1 quart bags on Amazon, and they're all of varying dimensions.
The TSA does not specify the exact size of the bag to be used, as long as it is less than one quart (946 ml or just under 1 liter). TSA agents are unlikely to pull out a ruler to meausre your bag, so as long as it is obvious that the bag contains less than one quart you should be fine.
According to Google, this is slightly less than a quart.
(6 inches) * (4 inches) * (2 inches) = 0.831168831 US quarts