Generally a Wikipedia entry will tell you the range of the aircraft, with the general formula above you can work out the average fuel consumption for the engines and then you can figure out the fuel capacity by combining the two. The actual fuel burn is very dependant on the power setting and figuring out which power setting was used is a function of altitude and temperature, aircraft weight and mission requirements. I wouldn't go down that route.
Also, keep in mind that you would never use the entire fuel capacity for mission purposes.