These are unisex, so all genders can use their general size. These sizes are for a fitted look- but not skin tight- that's why a 36inch t-shirt is recommended for size a size 8 whose actual bust measurement would be about 32inches.
Often, customers want a loose fit- most of the models are photographed in the next size up, so show a looser fit- so if you are a fan of the baggy comfy vibe, why not go up a size.
If you feel unsure, feel free to just purchase and write a bust/chest measurement in notes with a short description of how you'd like it to fit, and I'll message you if I think you'd prefer a different size.
Most designs can be requested up to 5XL, it's best to send measurements and fit preferences to get it right first time!