Body Type
Height: A person with a regular body type with a height above 5 feet is fit for a Standard Chair while a person lower than 5 feet can go with Petite. A person with a regular body type higher than 6 feet can go for Standard Chair with Tall Gas Lift
Stature: It is worth noting that the part that connects the backrest to the seat pan is shorter in Petite compared to the Standard Chair. A person with smaller stature (shorter legs and waist/torso can go for Petite Chair). Bigger or wider legs can sit comfortably in a Standard chair because it has a broader seat pan compared to Petite Chair
Desk Surface
It is important to remember that having your arms at the right height for your work surface is an important step in maintaining good posture at a desk or table. Those with higher desk needs to have either standard or tall lift depending on how tall you want to be. See measurements for heights for the lift. If you want a tall lift and have shorter legs, you may want to add in a foot ring so that your feet can rest and will not swing loosely.
Sitting Position
We tend to stay in a position when we deem comfortable. People who sit crossed-legged (yoga style) can enjoy sitting in a Standard Chair because of the wider seat pan. People who like to sit with the other leg on top of the other need to measure the height (from the bottom of the desk and legroom) so that they can estimate the needed height of the Gas Lift.
Comparison
A good way to determine your correct size gas lift is to find a seat that is at the right height for you, and to measure from the top of the seat to the floor (try building up seat height incrementally with a stack of books or magazines).
Disclaimer: This is intended to be a guide or reference only. Every person has different body types, measurements, sitting requirements, and other needs.