Guides · 11 min read

Eight hours in a chair that fits: reading OSHA's numbers against your own legs

OSHA has written down what an ergonomic chair is, in figures, and most of them are about your legs rather than your back. How to read seat height, seat depth and capacity against your own body, why a criss-cross seat breaks one of the rules on purpose, and the sentence about standing up.

The word ergonomic is printed on a great many chairs, ours included, and it is one of the few marketing words that a government agency has actually defined. The Occupational Safety and Health Administration's guidance for computer workstations lists what a chair has to do, and most of the list is about your legs rather than your back. Those figures read against your own body are below, along with why the chair we are known for breaks one of them on purpose, ending where OSHA ends, with the sentence about standing up.

Start with your feet, not the backrest

OSHA's first requirement is that the seat should let your feet rest flat on the floor, or on a footrest, with your thighs roughly parallel to the floor and your knees about level with your hips. That is a number, and it is the seat height. Sit on the edge of any chair with your feet flat and measure from the floor to the crease behind your knee; for most adults that is 16 to 20 inches. The seat height range on each of our chair pages is what to read it against. A chair whose lowest setting is above your knee crease leaves your feet dangling, which loads the back of your thighs; a chair whose highest setting is below it folds your knees above your hips, which loads the lower back. The gaming chairs on our shelf adjust through 3.9 inches, and the criss-cross chair through 4.7; the office chairs print their own range.

If the desk is fixed at 30 inches and the chair that puts your feet flat also puts your elbows below the desk, OSHA's answer is a footrest, not a compromise: raise the chair until your forearms are level with the desk, then put a footrest under your feet. A rolled towel works on the first day.

Then the elbows

The second figure is the elbow. OSHA's neutral posture has the upper arms hanging at your sides, the elbows bent between 90 and 120 degrees, and the forearms roughly parallel to the floor with the hands on the keyboard. Armrests, if the chair has them, should let your shoulders relax and your elbows stay close to your body; an armrest that is too high shrugs your shoulders for eight hours, and one that is too wide pulls your elbows out. That is why our chairs with flip-up arms exist: the arm goes up for typing and down for reading, and the chair slides under the desk lip either way.

The back, which comes third

The backrest should conform to the natural curve of your spine and provide lumbar support, which means a curve that pushes gently into the small of your back when you sit upright. OSHA prefers that the support be height-adjustable, so it lands on your lumbar rather than the chair's idea of an average one, and that the backrest recline at least 15 degrees from vertical and lock or hold under tension. The mesh and PU leather office chairs on our shelf carry that curve; the gaming chairs carry a separate lumbar cushion and recline to 135 degrees, which is past the 105 to 120 degrees OSHA draws for reclined sitting. A high back with a headrest is for that reclined posture and for nothing else; sitting upright, your head does not touch it.

The base, and the floor under it

OSHA asks for a five-leg base with casters that let the chair move easily, and every office chair on our shelf has one. The figure to read is the base width on the card, because a five-caster star is wider than the chair looks in the photograph, and it has to fit between the legs of the desk and roll on the floor you have. Casters roll on hardwood and laminate; on a deep rug they sink and the chair stops swivelling, which is the case for a chair mat or for the fixed-foot vanity chairs, which stand still on purpose.

The chair that breaks a rule on purpose

The criss-cross chair, the piece we are known for, has no armrests and a seat cut wider than OSHA's drawings. That is a deliberate break with the neutral posture, and it exists because the neutral posture is one posture and OSHA's own guidance says not to hold any single one for long. A wide armless seat lets you sit cross-legged for an hour, then feet down, then sideways to the window, and the low curved back supports the lower spine in the upright position and follows you in the others. It states a capacity of 300 pounds and adjusts through 4.7 inches of height. It is a worse chair than a mesh task chair for holding one perfect posture, and a better one for changing posture, which OSHA rates the more important of the two.

Capacity is our figure, and it is on the card

Every chair on our shelf prints the weight capacity we state: 250 pounds on the smaller mesh chairs, 275 on the gaming and dining chairs, 300 on the criss-cross chair and the PU leather chairs, 350 on some stools and waiting-room chairs, higher on the two big-and-tall seats. Read it against your own weight with a margin, and read it as a static figure for sitting; a reclined gaming chair with the footrest out balances differently, so it belongs on a hard floor. Where we state no capacity, the card prints none, because a figure we guessed would be worth less than a blank.

The sentence about standing up

OSHA's guidance ends with a sentence that most chair advertising leaves out: regardless of how good your working posture is, working in the same posture or sitting still for prolonged periods is not healthy, and you should change your working position frequently. Its list is short. Make small adjustments to the chair. Stretch. Stand up and walk for a few minutes. Do some tasks standing: reading, calls, meetings. A chair with lumbar support is a tool for the first item; a desk that rises is a tool for the fourth; and neither one is a treatment for a back that already hurts, which is a question for a doctor rather than a card.

A wide armless seat is a worse chair for holding one perfect posture and a better one for changing posture, which OSHA rates the more important of the two.

Reading a chair page in order

• Floor to the crease behind your knee, sitting with feet flat, against the seat height range on the page.
• Elbow height with the upper arm hanging, against the desk top; a footrest closes the gap if the desk is fixed.
• Lumbar curve and recline: a height-adjustable support and at least 15 degrees of recline, locked or under tension.
• Base width on the card against the space between the desk legs, and the floor under it.
• Stated capacity against your weight, with a margin.
• A plan for standing up, because the chair is not one.