These are body measurements. All measurements are in inches.
Shirts & Tops

Bust Waist Shoulder
 xs 32-33 26-27 13.75
 s 34-35 28-29 14.25
 m 36-37 30-31 14.75
 l 38-39 32-33 15.25
 xl 40-41 34-35 15.75
 xxl 41-43.5 36-38 16.5
 
Dresses

Bust Waist Hip
xs 32-33 26-27 35
s 34-35 28-29 37
m 36-37 30-31 39
l 38-39 32-33
41
xl 40-41 34-35
43
xxl 42-43.5 36-38
45.5
Jumpsuits

Bust Waist Hip
xs 32-33 27-28 35
s 34-35 29-30 37
m 36-37 31-32 39
l 38-39 33-34 41
xl 40-41 35-36
43
xxl 42-43.5 37-38
45.5

Blazers

Bust Waist Shoulder
xs 33 30 13.5
s 35 32 14
m 37 34 14.5
l 39 36 15
xl 41 38 15.5 
  
Trousers

Waist Hip Length
xs 26-27 35.5 34
s 28-29 37.5 34.5
m 30-31 39.5 35
l 32-33 41.5 35.5
xl 34-35 43.5 36
xxl 36-38  45.5 36.5
 
The following chart will help you match our size scheme to your usual size

Qua xs s m l xl xxl
UK 6 8 10 12 14 16
US 2 4 6 8 10 12
Italy 38 40 42 44 46 48
France 34 36 38 40 42 44