Divide the 747's maximum fuel capacity in gallons by its maximum range in statute miles to calculate the aircraft's fuel economy as gallons per mile. As an example, a 747-8 has a maximum fuel capacity of 64,225 gallons and a maximum range in statute miles of 9,206. Dividing these figures gives you 6.98 gallons per mile.
Multiply the result from Step 1 by the number of miles the aircraft will be traveling. For example, if the aircraft will be traveling 2,000 miles, multiply 6.98 by 2,000 to get a result of 13,960.
Add 20 percent to the number of gallons calculated in Step 2 to account for reserves and unknowns, such as slower-than-expected ground speed. For example, multiply 13,960 by 0.2 gives you 2,792. Add 2,792 to 13,960 to get a sum of 16,752. The amount of fuel needed for a 747-8 aircraft going 2,000 miles is 16,752 gallons.
