Calculating fuel and total weight.

This forum section is more for the NEW FS that's not yet released, but:

Fuel needed is fuel burn rate times the flight time. Don't forget to allow for the different burn rates during taxi, climb and descent. You can also fill your aircraft (menu page), take off and fly for an hour, then look at the menu for how much fuel you've burned and calculate the burn rate from that.

Total aircraft weight is empty weight plus payload and crew plus fuel. For any more than that you'll need to tell us what aircraft, and you'd need to supply the above information.

Note that fuel burn rate is usually, depending on the aircraft, etc., either gallons/liters per hour or pounds per hour, depending on the fuel information that you have, and of course it's different for each aircraft type. Also note that there's a pretty good chance that the burn rate in the sim doesn't necessarily match that of the real life counterpart, depending on how the developer did his simulation.

In FS or P3D the aircraft/fuel menu can help you. I think there is a menu related to weight and balance, but it's been a long time since I looked at that. A lot of information is also in the aircraft.cfg file for the specific aircraft.

Little Navmap has a data collection feature where it will log your fuel burn, speed, etc. while you're flying. It saves the data to an aircraft profile and then when you make a flightplan it will tell you how much fuel you'll need including reserves, alternate, etc. You can improve the accuracy of the collected data over a number of flights, it can collect new data and merge it with the previously collected data, it averages the figures, the more flights you do the more accurate it becomes. I've been playing with it recently and for example on one flight I did LNM predicted I'd have 2160 lbs left after arriving at my destination, in actuality I had 2138 lbs. That's pretty close considering the block fuel for the flight was 4632 lbs. In this example I was flying the Carenado 560XLS on a 575 nm flight.

Read more about it here:

https://www.littlenavmap.org/manuals/littlenavmap/release/2.4/en/TUTORIALPERF.html