You have to either do simple math, or get a Ratio-Rite mixing cup. They have columns of numbers on them based on how much fuel you are mixing into. Find the column that says "5 Gal." at the top, then fill to the line in that column that says "40:1". There are columns for most all quantities from 1 gallon through 5 gallons. Those cups cost less than $3 at most shops. You can also get a cap for a buck or two that snaps on and keeps the oil residue from getting all over things and also keeps dirt from getting in. A good investment, IMO. (The cup and the cap) :thumb: