The internal dimensions of the chair (seat height, width and depth, and backrest height) need to match the size of the user to ensure adequate support.
When seated, the support that the chair gives users from underneath should be evenly spread beneath their bottom and legs, with no particular points of pressure.
The support to the back should enable the user to relax, helping them to maintain a safe and comfortable position, again with no particular points of pressure.
Do not forget the overall size of the chair in relation to the room, so check the overall dimensions of the chair if space is limited. If the chair is going to be reclined regularly, make sure that there is sufficient space behind the chair.