The aluminium alloy 5754 H-111 is a high-strength alloy with a remarkable corrosion resistance, particularly to seawater. It is widely used in the aerospace, marine, and automotive industries. In this work, the influence of fracture toughness methods applied to two thin aluminium sheets with different thicknesses (1.8 mm and 5 mm) was analysed. The first method was the essential work of fracture (EWF) method. It was applied at room temperature at a deformation rate of 1 mm/min with a double-edge notched tensile specimen (DENT) to measure the fracture toughness ( $w_e$) of a material with ductile damage based on the stored energy of the body. The second method was a compact tensile test (CT) to determine the linear elastic fracture toughness. For the EWF, DENTs of 4, 6, 10, 12, and 14 mm were used in the centre section. The EWF values were 273 kJ/m² and 63 kJ/m² for the aluminium sheets with thicknesses of 5 mm and 1.8 mm, respectively. The surface energies J_IC determined using CT were 34.5 kJ/m² and 10.6 kJ/m², respectively, for these sheets. These values are highly similar. Furthermore, the percentage errors of the elastic EWF were 5.8% and 8.4%, respectively, for the two thicknesses. The fractures were of the stress types in which the pits and voids grow in conjunction. In addition, both deep and isolated large dimples were well distributed in the aluminium, which is the main ductile deformation concept.