This paper presents a flame length methodology that mimics the human eye or camera using a CFD framework to calculate the flame structure. A parabolic flow model which accounts for turbulent combustion, soot kinetics and visible radiation distribution is extended to predict both rim-stabilised and lifted jet fires. The model is calibrated using a selected set of jet fire experiments and then validated against a wider range of data. Good agreement over a range of scales is demonstrated particularly when taking the degree of repeatability of the experiments into account. The flame length prediction is found to be insensitive to receiver location so long as the receiver is one or more flame lengths from the fire