This classroom activity uses Legos® to visualize different metrics for analyzing efficiency and waste in chemical reactions. In introductory courses, or even specific green chemistry classes, students encounter formulas for yield, selectivity, conversion, atom economy, E-factor, and many other waste quantification schemes. This activity helps to visualize these often nebulous concepts. The common green chemistry metrics rely either on number of molecules, number of atoms, or molecular weight. In this activity, individual bricks represent atoms, and we can piece them together in a manner relatively true to their bonding arrangements. The number of connections points on each brick represents that atom's molecular weight (2x6 piece = 12 connections points = 12 AMU = carbon). A completed model represents a molecule. By comparing the number of bricks, models or connection points on either side of the numerator and denominator in the various waste quantification schemes, students can easily visualize these common metrics.