Ever since I bought my motorized bike, I 've relied upon guessing the right amount of oil to put into a fuel mixture. Or if I bought the right oil container, I would have used the measured markings on the side of the bottle. After some looking, I found this: Amazon.com: RATIO RITE CUP - Kam-Tech -: Automotive
The Ratio Rite measuring cup has markings for ratios from 16:1 to 70:1. Markings for 1, 1.5, 2, and 2.5 gallons. Since buying this, I'm sure that I'm mixing the right ratio of oil to gasoline.