I usually wear a size medium, but this jacket was purchased as a small because naturally puffer jackets are on the larger spectrum. Plus, I purchased this jacket with the idea in mind that would only be wearing one base layer beneath it. If I was planning to wear heavier garments, such as a sweatshirt or a hoodie. I probably would’ve went with a medium. But the jacket itself is so extremely warm that I knew I would only need a thin base layer beneath it. Took it on one trip. Worn once and since then I have intentionally gained weight which I don’t intend on losing.