Most modern airliners measure fuel by weight, usually in pounds or kilograms, rather than by volume in gallons or liters. This is because the volume of a given mass of fuel can change with temperature.

Fuel is stored in the aircraft’s fuel tanks, which are typically located in the wings and sometimes in the fuselage. These tanks are designed to withstand changes in temperature and pressure, but the fuel inside them can still expand or contract with changes in temperature.

When fuel is stored at a higher temperature, it expands and takes up more volume, while at a lower temperature it contracts and takes up less volume. If fuel is measured by volume rather than by weight, this can lead to inaccurate fuel readings and affect the accuracy of fuel consumption calculations.

By measuring fuel by weight rather than by volume, the effect of temperature changes on fuel volume is eliminated, and the fuel consumption calculations can be more accurate. The weight of the fuel is typically measured by a fuel quantity system that uses sensors located in the fuel tanks to measure the weight of the fuel in each tank. The readings from these sensors are then processed by the aircraft’s flight computer or fuel management system to provide real-time information on the remaining fuel and fuel consumption rate.

In addition to weight, the fuel sensors in modern airliners may also measure other parameters, such as fuel temperature and density, to provide more accurate fuel readings and improve fuel efficiency. By measuring fuel by weight and monitoring other fuel parameters, modern airliners can optimize fuel consumption and ensure that the aircraft has enough fuel to complete the planned flight safely and efficiently.