Adjust your chair to the correct height (so that your feet are resting comfortably flat on the floor, and your legs have a slight downward slope i.e. the top of your leg where it meets your body should be slightly higher than the top of your leg at your knee. Measure the distance from the seat (after you are sitting in it i.e. taking into account the compression of the seat material) to the ground in inches, and it is also helpfuly to have your height when standing.

In general...

If you are under 5'4" tall, you may consider the Short cylinder - range is 15" to 18"
Specifically, if your seat height is less than 16" above the ground, you may want to consider purchasing the short cylinder.  If you are under 5'2", we recommend seriously considering purchasing the short cylinder, and measure the seat pan height you require.

NOTE: If you have to reach up to get to your worksurface (i.e. keyboard, mouse, desktop, etc.), you are better off to get the standard cylinder rather than overextending to work. Similarly, your primary viewing area (usually the computer monitor or document holder) should be at an appropriate height such that you don't have to tilt your head/neck back to see this area. Of course if you purchase a standard cylinder, your feet will 'dangle' so this will also necessitate the purchase of a foot rest to provide proper support and ensure comfort. However it is better to have a (taller) chair that puts your working area and viewing area at the correct height and requires a footrest than to get a 'correct' shorter chair which puts you at the wrong height to see your monitor and work on your keyboard.

If your are in between 5'4" and 6'2" tall, you usually should get the Standard cylinder - range is 17" to 20"
Specifically, if your seat height is in between (i.e. 16" - 20" above the ground) we recommend the Standard cylinder.

If you are over 6'2" tall, you should consider getting the Tall cylinder - range is 18" to 24"
Specifically, if your seat height is more than 20" above the ground, you may want to consider purchasing the tall cylinder, and if you are over 6'5" tall, we recommend seriously considering purchasing the tall cylinder.