Finite element analysis and analytical geometric analysis are two active approaches to calculating local wall thicknesses in simple vacuum formed parts. FEA requires substantial computational skills and mainframe computer access. Analytical geometric analysis is usually restricted to relatively simple shapes such as cones and wedges. In this paper, an easy-to-learn protocol is proposed for calculating wall thickness of relatively complex shapes. A portion of the protocol is based on the Fukase blow-molding scheme. The protocol is applied to a rectangular cookie tray with wall thickness accuracies to within 30% for most sections of the part. 3D corner agreement is excellent but vertical 2D corner agreement is not good.