Directions to how to mix gas and calculate volumes:
How to figure out mix ratios: If you meed to mix at 30:1 or 50:1 or whatever and you want to know how much oil to mix in the amount of gas you have, first you need like units - ie: gallons (gal) and gallons or ounces (oz) and ounces. Normally gas is in gallons and 2 cycle oil is in ounces, so we need to convert one to the other - just convert gallons to ounces.
There are 128 oz in a gallon.
128 oz of gas mixed 50:1 = 128oz / 50 parts = 2.56oz When you add in the oil there will be 51 total parts - this is not a problem.
Don't over analyze this: The engineers of the motor's for our weed wackers tried to make it easy on us, so any redneck could have a long career in the mowing business.
Or for the math people:
G = Gallon(s) of gas you have.
M = Mix Constant (ie 50 if you are using 50:1)
G * 128
------- = oz's of oil to add
If you are still confused just use the chart below... find how much gas you got on top and your ratio on the side and meet them to find the amount of oil you will need. "In ounces (oz)"