Shoulder: Measure from one shoulder to the other.
Chest: Measure around the fullest part, place the tape close under the arms and make sure the tape is flat across the back. 
Length: Measure from the highest point of the shoulder to the hemline. 
Sleeve: Measure from the shoulder seam to sleeve end

Waist: Measure around your waist where your pants usually fall. Keep one finger between the tape and your body to ensure an accurate fit.
Hip: Measure at the fullest part of your seat, keeping the tape parallel to the floor.
Length
: Measure from the top of the waistband to the bottom of the hem.

Sizes can vary from 2-3 centimeters because they are measured by hand. 1inch=2.54cm
The size matched on a label can differ from the one you have ordered.