The bottle should say how many gallons of gas to mix with that bottle. I believe the 6.4 oz. bottles are for 5 gallons of gas. I would only use 4 gallons of gas for each of those bottles.
Do yourself a favor, and DON'T mix partial bottles! I've seen guys try to guess how much is 1/2 a bottle so they can only get 2.5 gallons of gas and those are the guys who burn up saws.
Several have stated and I agree, if you use a quality oil mixed between 32-1 and 40-1, you can use it in EVERY air-cooled 2-cycle engine you own. I have Echo and Stihl equipment, weedeater, blower, saws, etc. and I run the same gas in ALL of them. Have for 20 years, and NEVER had any type of fuel related problem. People (and manufacturers) try to complicate it, but it all boils down to enough lube to save the motor without fouling the plug.
OK, I've started to repeat myself, if I answer any more questions on this I might start to get frustrated. 'Nuff said.