"20 MPG is about 0.1 square millimeters," according to https://what-if.xkcd.com/11/ https://what-if.xkcd.com/11/. "If you took all the gas you burned on a trip

"20 MPG is about 0.1 square millimeters," according to https://what-if.xkcd.com/11/ https://what-if.xkcd.com/11/. "If you took all the gas you burned on a trip and stretched it out into a thin tube along your route, 0.1 square millimeters would be the cross-sectional area of that tube." It's simple dimensional analysis (https://xkcd.com/687/ https://xkcd.com/687/).