Everything is meant to be blousy. Don’t be afraid to order beyond your size if you like things big. Generally, dimensions are listed with the garment.
For Button-Downs and Dusters:
XS/S dress size 2-4
S/M dress size 6-8
M/L dress size 10-12
L/XL dress size 14-16
XL+ usually fits up to a 4XL, if unsure, just message me before buying
For Pullovers, Sweater Cardigans, Dusters, Sweater Coats and other tops/tunics:
XS/S fabric circumference is generally 38-42 inches
S/M fabric circumference is generally 42-45 inches
M/L fabric circumference is generally 45-50 inches
L/XL fabric circumference is 48-54 inches
XL+ fabric circumference is 55-59 inches
These are general estimates.