Additive Manufacturing (AM) technologies such as Laser-Based Powder Bed Fusion (LB-PBF) enables fabrication of complex lattice structures. However, LB-PBF processes inherently induce dimensional variation between idealised and as-manufactured specimens. This research proposes and implements a method to characterise the structurally relevant geometric properties of as-manufactured strut elements; as demonstrated to characterise the effect of LB-PBF material (aluminium alloy and titanium) and geometric design parameters (polygon order, effective diameter and inclination angle) on the stiffness and strength of as-manufactured strut elements. Micro-computed tomography is applied to algorithmically characterise the as-manufactured variation and identify a threshold below which additional geometric resolution does not result in increased part quality. This methodology provides an algorithmic and robust Design for AM (DFAM) tool to characterise the effect of manufacturing and design parameters on the functional response of AM strut elements, as is required for certification and optimisation.