How is vehicle fuel economy measured?

Fuel economy is measured by: Laboratory testing on chassis dynamometer following standardized drive cycles while measuring either fuel consumption directly (gravimetric or volumetric) or calculating from exhaust carbon content (carbon balance method); Real-world testing using fuel flow meters or tank-to-tank measurements; and On-board fuel economy displays from ECU calculations. Laboratory tests occur under controlled temperature and humidity. Results are adjusted using correction factors and labeled according to regional requirements (EPA, WLTP). Coast-down testing determines road load coefficients for dyno setup.