They make containers that are designed to help you mix the oil & gas properly.
It should have several different mixture ratios marked on the container. You choose the one you want & then fill it up w/ the oil until you reach the mark for however many gallons of gas you are using.
I run 32.1, Its nice to be able to just pour some oil in there and mix it quickly and accurately.
I highly recommend one. They are cheap enough and it might even save your motor one day. Its easy to screw up if you are not paying attention.