Size

The bottom cushion should not be too long for you to get fully back in the seat, with the back of your buttocks behind the small of your back. This is often a problem in 'executive' chairs.

Adjustability

With fixed-height desks, only a small amount of height adjustment is needed to suit nearly everybody (you should set the elbow height to match the desk, then as a separate issue get a footrest to suit your lower leg length).

Separate height adjustment of the back is important if it has lumbar support built in. If the seat has tilt adjustment, it should be a 'knee tilt' design which limits the change in height at the front of the cushion.

Armrests definitely should be height-adjustable if they are fitted. Fixed-height armrests are nearly always too low, encouraging you to slump down to them.

Lumbar Support

Most of the office chairs in use today do not provide correct lumbar support. This is even true of seats which claim ergonomic design. Most seat-backs either have no lumbar shape, or it is a small bump set too low - behind the pelvis rather than the lumbar vertebrae.

Lumbar pads are cushions that attach to the back of seats in order to provide better support to the lower back. More information can be found on the Lumbar Supports catalogue page or on the Open Ergonomics Back Support page.

Armrests

Armrests must be at the correct height for the user. Too high and the user will tend to work with their shoulders hunched. Too low and the users will slouch in their seat. Most fixed armrests are set too low, so adjustability is more or less essential. If you need to you can build up the height of fixed armrests by wrapping foam around them.

Armrests must be short enough to allow the chair to get close enough to the desk. This is generally little more than half the length of the bottom-cushion.

Not everyone likes armrests, but those who do can benefit from the reduction in arm weight hanging from the shoulder. This reduces the static loads on the spine and buttocks.

Shape

The cushion should be flat. Avoid cushions which have a rise at the back as these will compress the buttocks, also avoid 'waterfall front ' seats which have an extended slope at the front - these give no support but can prevent you sitting fully back in the seat.

The seat back should have a smooth lumbar support curve which is at least 260 mm in length, and adjustable for height. Unfortunately we do not know of such a chair in production. Choose a shape which is simple and spreads support over the largest possible area, to reduce pressure on the skin. All the office chairs we have encountered would be improved by an add-on lumbar support. You don't need lateral support in an office chair.

Cushioning

One of the ways cheap chairs are made possible is by using cheap low-density foam in a thin layer. Check this by pressing your fist hard into the cushion and backrest. If your knuckles easily 'bottom out' onto the hard surface underneath the foam then it won't last.