For copper busbars, IEC 61439-1 and common engineering practice recommend 1. The busbar sizing calculator determines the required busbar dimensions based on the continuous current rating, short circuit withstand, and thermal limits for switchgear assemblies. The current rating is calculated from the conductor cross-sectional area, material (copper or aluminium), and maximum. To calculate Busbar Current, enter the width (mm), thickness (mm), and material carry capacity factor (amps/mm^2). 2 * Busbar width in mm * Thickness in mm Amps Aluminium: Aluminium busbar current carrying capacity = 0. Supports rectangular and round shapes.