About 14% of gross is what I run for gas for my one truck (F350 dually - gas guzzler) and the gas for equipment. But as others have stated its pretty much a meaningless number for someone else. Most of our lawns are pretty consolidated to a handful of areas which helps cut down on the gas use. We cut about 130 a week, then we do leaf removal in winter, not as busy as lawns but still pretty steady.
2008 F-350 Super Duty Dually gas guzzler
14x7 landscaping trailer
12x6 P&T hydro dump trailer w/leaf box
We run Gravely ZTRs, Honda 21"s, Kawasaki trimmers, Redmax Backpacks, LittleWonder loader