I am a 36 (barely) C, meaning I sometimes wear 36 or 38 B. I am nearly spilling out of this. It's super cute and pretty comfy. I got a large, maybe I could have gone up a size, but then maybe it would be too lose around the band area? Large is my normal athletic bra size. It fits comfortable mostly, the cups are just smaller than I was expecting, so if you are a larger cup size be prepared for some major cleavage. I've only worn it once and plan to try it without the pad inserts next time.
I would say this bra is true to size, I have tried an xs in the Y back sports bra and it was way too tight. I ordered a small in this and its a little too loose.
Pattern Free Feeling Strappy Sports Bra Low Impact