Whats the average size of a chevelle gas tank... since my feul gauge does not work... i keep filling it up.. but i dunno when i've really pushed it..i think the most i have put in is 12 gallons.

I assume you're asking about a 70 in particular? The owner's manual says all 70 Chevelles have a 20 gallon (approximately) capacity except station wagons which have 18.5 (approximately).

For the average:
There were 488,019 total production of Chevelles in 1970 (including Canada).

Of these, 447,357 were non-station wagons that calculates to 8,947,140 gallons of gas to fill them up.

The 40,662 station wagons will take 752,247 gallons of gas to fill those.

This gives you a total of 488,019 Chevelles requiring 9,699,387 gallons of gas or an "average" of 19.875 gallons each (approximately). :D

If your fuel gauge doesn't work (or is suspect like mine) and your speedo and/or odometer is accurate, make note of your mileage and consumption a few "normal" fillups. Once you've gotten your average miles per gallon, you can use that to gauge when you're getting close to needing fuel. Works for me.

20 gallon.

I was searching for the gallons and i found this

http://www.mmsacc-stainless.com/html/gas_tanks.htm

Both of my Chevelles are 20 gallons. I've put 18.5 gallons in the 70 on more than one occasion. I don't htink I have ever put more than 14 in my 69. I think the gauges is a little suspect just as Dale said.

well actually.. my speedo AND odometer is suspect as well. The fuel sending unit is reading 250 ohms!! I gotta take the gauges out to id them...need hands for that.. they are all after market autometers, but the fuel gauge SHOULD still run 0-90 ohms, but i need the part number to be sure. I also KNOW that my odometer is clicking twice as fast as it should.