AlabamaJack said:cheat if you want...
But...I don't think my 5 gallon nursery containers actually hold 5 gallon volume....more like 4...
You're correct. I see this come up now and again, but nursery containers started shrinking at some point, but no one bothered to change what they call them. I guess you can sell a shrub for more money when you call the pot its roots are in 5 gallons instead of 4.3 gallons.
I use a lot of food grade 5 gallon buckets (pickle buckets, lately) to plant things in because I can get them cheap ($2), they're sturdy, relatively safe from contaminates, and they have a handle if I need to pick them up and move them.
I couldn't sleep because what I said will give an approximate volume of the container so to be more accurate in determining the volume of the container....
*rolling my eyes*