How do you figure how much soil you need?

[talos4]

How many 1.5 cubic feet bags of soil would I need to fill ten 3 gallon containers? I'm terrible at math. I would like to use Fox Farms Ocean Forest. Each bag is 1.5 cubic feet

 

[ZMAN]

a 2 cubic bag fill 6 3 gallon pots for me but i mixed almost 7 qts of perlite too.
so maybe 3?