I figured this math was pretty solid, but using other numbers given by the game I have obtained a very similar result. The engine used for this math is the J-33 "Wheesley" turbofan engine due to its convenient numbers. Now, most of you probably know that the equation for specific impulse in seconds is where F is the thrust (in newtons), g0 is gravity (9.81 m/s2), Isp is specific impulse in seconds, and m is fuel flow in kg/s. In order to find the fuel flow, I rearranged the equation to F/g0/Isp = m. With the wheesley, f = 120,000 newtons, g0 = 9.81, and Isp = 10500. So, the new equation is 120,000/10500/9.81 = m. Do the math, and you get 1.164991990680064. Divide 1.164991990680064 by the flow listed in the game (2.33U) and you get 4.999965625236327, or approx. 5 kg.