Jet A fuel, a specialized kerosene-type fuel used almost universally in turbine-engine aircraft, is the energy source that makes modern air travel possible. Knowing the exact weight of this fuel is far more important than knowing its volume for aviation safety and performance. The precise weight of the fuel directly affects an aircraft’s maximum payload capacity, its stability during flight, and its overall operational range. The aviation industry relies on highly specific measurements and calculations to determine the true quantity of fuel on board.
Standard Density and Specific Gravity
The question of how much Jet A fuel weighs per gallon has a variable answer, which is why a standard reference point is used. The aviation and petroleum industries define a standard density for Jet A and Jet A-1 fuel at a temperature of 15° Celsius (59° Fahrenheit). This standardization allows for consistent comparison and accurate transactions worldwide.
At this standard temperature, the nominal density of Jet A fuel is approximately 0.80 kilograms per liter (kg/L). Converting this metric standard into the US customary unit yields a weight of about 6.75 pounds per US gallon. Individual batches of fuel may vary slightly from this figure, but 6.75 lbs/gal serves as the widely accepted baseline for flight planning and design purposes.
Specific Gravity (SG) is a related, unitless value that serves as a reference point for the fuel’s density. SG is calculated by dividing the fuel’s density by the density of water, both measured at the same standard temperature, typically 60°F. Since Jet A fuel is lighter than water, its specific gravity is less than 1.0, generally falling in a range between 0.80 and 0.82.
The Impact of Temperature on Jet A Weight
The weight of a single gallon of Jet A fuel is not constant because liquids are subject to thermal expansion and contraction. The actual mass of the fuel molecules does not change, but the volume they occupy expands when the temperature rises and contracts when it drops. This volumetric change directly alters the density, or weight per unit volume, of the fuel.
For instance, a US gallon of Jet A fuel at a frigid 0°F can weigh approximately 6.91 pounds, while that same volume of fuel on a hot day at 100°F might only weigh around 6.58 pounds. This difference of over a third of a pound per gallon can become substantial when dealing with the tens of thousands of gallons a large airliner carries. The aviation industry must account for this phenomenon to ensure flight safety.
This is precisely why the standard 15°C/60°F reference point is so important for density measurements. Fuel temperature can fluctuate significantly from the moment it is pumped from a cool underground storage tank to when it sits in an aircraft’s wing tank on a sun-baked runway. Aviation protocols require a precise temperature correction to determine the true mass of the fuel, regardless of the ambient conditions. Therefore, the weight per gallon is an operational variable, while the total mass is the fixed quantity required for the flight.
Converting Volume to Usable Fuel Mass
Aircraft systems and performance calculations rely on the mass of the fuel, not the volume, because the energy output of the fuel is directly related to its mass. Engine performance, range, and aircraft balance are all computed based on pounds or kilograms of fuel, which remains constant regardless of temperature. A volume-based measurement, such as gallons or liters, would be unreliable for flight planning due to the temperature effect on density.
To ensure accuracy, aircrews and fuelers must employ a conversion process when refueling an aircraft. The fuel is delivered by volume, but the fueler measures the fuel’s temperature at the time of delivery using a specialized thermometer. This measured temperature is then used in conjunction with a density meter reading or standardized tables, such as the ASTM-IP Petroleum Measurement Tables.
These tables provide a Volume Correction Factor (VCF) that converts the measured volume at the current temperature back to the reference volume at 15°C. By applying this correction factor, the fueling team can calculate the exact mass of fuel delivered. This methodology guarantees that the aircraft receives the necessary weight of fuel for the flight, ensuring that performance calculations remain accurate.