Most of you have newer rigs with automatic oil mixtures, I think. But for those who do not and are not sure about ratio's when at the gas pumps.....I thought perhaps I would share this web site.
You can plug in numbers that will give you the ratio's for a 50:1 mix
I made a chart for my own use for from 5 gallons to 25 gallons in 1 gallon increments. Not sure if I'm going to put a copy in the rear deck lid to use when I have to get the oil and ethanol additives out or put in my pocket but, in any case - no more having to stop and figure.
Ex: have to put in 17 gallons of gas, had to figure how much oil to add to the gas.
Hope it might help some: Gas/Oil Ratio Chart