An important step before any safe flight is to calculate how much fuel will be needed. Even with mixed units, FlightMath can compute fuel capacity, burn rate, and time.
Clicking on the Fuel tab will give you a window like this:
This tab allows you to calculate an unknown value from two known values. The three variables are Burn Rate, Capacity, and Time. The units for Burn Rate and Capacity can be set separately. Burn Rate can be set, using the corresponding pop-up menu, to Gallons per Hour or Liters per Hour. Likewise, Capacity can have the units of Gallons or Liters. Time is always given in hours and minutes.
The diamond to the bottom-left of the window indicates whether the values of Burn Rate, Capacity, and Time are up-to-date. A white diamond like this:
indicates that a calculation has been made and the variables are all correct. A darkened diamond like this:
indicates that something has been changed and the values of Burn Rate, Capacity, and Time may not be correct. Before reading any values from the respective text fields, make sure that you have a white diamond indicating that your data is up-to-date.
To make a calculation, you need to know two of the three values. For example, if you want to know how long you can fly on one tank of gas (time), then you need to know the aircraft's fuel burn rate and fuel capacity. Say your aircraft burns 4.8 US Gallons/Hour and you have 12 gallons of usable fuel. In the text field labeled Fuel Burn, enter 4.8 and select US Gallons/Hour in the Burn Rate units menu. Likewise, enter 12 in the Capacity text field and set the units menu to US Gallons. Finally, click the upper Calculate button, next to the Minutes text field. You will see 2 hours and 30 minutes in the Time text fields. This is how long you can fly on 12 gallons of gas.
In each of the menus that specify units, you may do a conversion by selecting one of the menu options preceded by a "->". This will automatically convert the value in the text field from the previously selected units to the units specified after "->". This feature is provided as an easy way to do conversions, but you don't have to use it to do fuel problems. FlightMath will automatically take all units into account.