The Acoustic Emission (AE) technique has been shown as capable in detecting and locating fatigue crack damage in metallic structures. However there are significantly fewer studies investigating its potential for fatigue crack length estimation. Information on the extent of crack growth would enable prediction of the remaining useful life of a component using well established fracture mechanics principles. This would improve the prospects of AE for use in structural health monitoring applications where detection and monitoring of crack lengths is required. A new approach for deducing absolute crack length has been developed based on correlations between AE signals generated during fatigue crack growth and corresponding cyclic loads. An empirical model to generate crack length was derived using AE data generated during fatigue crack growth tests in 2 mm thick SEN aluminium 2014 T6 specimens subject to a tensile stress range of 52 MPa and an R ratio of 0.1. The model was validated using AE data generated in separate tests performed with a stress range of 27 MPa. The results showed that predictions of crack lengths over a range of 10 mm to 80 mm can be obtained with the mean of the normalised absolute errors ranging between 0.28 and 0.4.