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Specific thrust is a way to determine the efficiency of a jet engine regardless of the size of the engine. The specific thrust is calculated by dividing the thrust created by the engine by the mass flow rate of the air (meaning how much air is flowing through the engine in a given amount of time). If one were to compare just the thrust of two different jet engines, most likely, the bigger engine would create more thrust. But by comparing the specific thrust of two engines, one can determine which one is more efficient, even if one engine is much larger than the other engine.