“We only carry sizes one, three, and five. You could try Sears.” Anyone who groaned at that Mean Girls line knows that women’s clothing sizing practically requires a Ph.D. in physics to comprehend. Why are you a 0 at Banana Republic but a 10 at H&M? What dark arts are being practiced here? Today’s Wall Street Journal sheds some light on sizing sorcery, reporting on the rise of so-called “alpha sizing,” meaning using small, medium, and large designations as opposed to numbers. More retailers are adopting it for a very simple reason: It’s way cheaper. “If I only have to build four sizes instead of eight, my supply chain is going to be much more efficient,” one consultant explained to the paper. However, merging a 6, 8, and 10 into a medium is going to result in sizing headaches for many customers (not to mention the problems with alpha-sizing bras, which many brands are adopting as common practice). According to the WSJ, megachains like Zara, Old Navy, and Uniqlo use the alphanumeric system, but there are some holdouts: Activewear chains Athleta and Lululemon are sticking with numbers for now.