Regarding the company’s efforts, Watson shared on Instagram, “I love their mission to inspire us to think secondhand first and create a more circular fashion future.” The calculator is just one of the company’s many initiatives to educate its consumers. Every year since 2013 the company has released annual reports about the resale market and how it’s shifting; this year thredUP discovered that the secondhand market will reach $51B in five years, while the resale market has grown 21 times faster than the retail apparel market over the last three years. While shopping secondhand is infinitely better than buying new clothes, the most sustainable thing you can do is rewear the stuff you already own.