Here is the general rule for those who want to know: 1 gal = 1oz 2 gal = 2oz 3 gal = 3oz This sometimes varies a few grams in either direction. Of course there are some differences and exceptions but these are the general rules. You should also know that corresponds to plant height as well. You want about 1 gallon of space for each 12" of growth. Growing Ebb & Flow trays or Ebb & Grow buckets with Hydroton etc, bypasses the general rule. What are your experiences?