A fuel gauge is the dashboard instrument in a vehicle that shows you how much fuel is left in the tank. A sensor in the fuel tank measures how much fuel is inside. It sends this information to the gauge on your dashboard. As you drive and use fuel, the needle or number goes down. When fuel is low, a warning light (usually a gas pump icon) turns on.
A fuel gauge of a Citroen Xsara, the car is turned off or out of fuel. © Wikimedia.org/Santeri Viinamäki, CC BY-SA