Determinig some values

Good evening ladies and gentleman;I have started to create some flight plans and I would like to know if you can help me out to explain how can I determine the following information on a particular aircraft [e.g Carenado Centurion or other TurboPro]Climb: Climb Fuel Burn Rate in Gallons per hour.Cruise: Cruise Fuel Burn Rate in Gallons per hour.Descent: Descent Fuel Burn Rate in Gallons per hour.Is there any formula to get this info. Have you developed any technique or does anybody know a way to do it and if so, how accurate it is?For instance, for the Climb Fuel Burn Rate, I have learned that it can be done by dividing the fuel flow at 75% powwer by .75. How accurate is this?I woudl appreciate if you can gibe some hits in how to do that?Regards,Juliet LimaKLGA