Measure these six things before you buy anything

Most home offices fail in week two. Not because the gear was bad, but because it was bought before anything was measured.

A chair cannot fix a desk that is two inches too tall. A second monitor cannot fix a desk too shallow to sit back from. Lighting cannot fix a screen that faces a window. So take the numbers first — all six fit in ten minutes, and you need a tape measure and the chair you already own.

#	Measure	What it decides
1	Elbow height, seated	Desk or keyboard height. The most important number here.
2	Popliteal height	Seat height, and whether you need a footrest.
3	Eye height, seated	Monitor height.
4	Arm's length	Minimum monitor distance.
5	Desk depth	Whether that distance is even possible.
6	Knee clearance	Whether you can sit square to the desk at all.

1 and 2: elbow height and seat height

Sit back, feet flat, thighs roughly parallel to the ground. Let your shoulders drop and bend your elbows so the forearms are level.

• Floor to the underside of your elbow — that is your seated desk height.
• Floor to the crease behind your knee, plus an inch or two if you wear shoes at your desk — that is your seat height.

OSHA describes a neutral seated posture as feet flat on the floor or a footrest with the thighs roughly parallel to the ground. Clinically, an angle slightly over 90 degrees at the knee — around 95 to 105 — tends to be more comfortable, because it takes pressure off the back of the knee.

The full desk-height method, and what to do when the desk is fixed, is worth reading if this is the number that came out wrong.

3 and 4: monitor height and distance

OSHA puts the preferred viewing distance at 20 to 40 inches from eye to screen. Arm's length is the fast version — sit back, reach out, and your fingertips should just brush the screen.

For height, put the top line of the screen at or just below eye level, with the centre of the display 15 to 20 degrees below horizontal. In practice: sit up, look straight ahead, and your gaze should land on the top third of the screen.

Larger screens scale differently. A useful rule is a viewing distance of one to one and a half times the diagonal — so a 27-inch monitor wants 27 to 40 inches of air in front of it.

5: desk depth, the number nobody checks

Everyone measures the width of a desk. Depth is what decides whether the setup works.

Here is the arithmetic that catches people out. Put a 27-inch monitor on its stock stand on a 24-inch-deep desk. The stand eats depth, the screen sits forward, and you are left with roughly 14 to 16 inches between your eyes and the panel. That is half the recommended distance, and no amount of chair adjustment recovers it.

Desk depth	What it supports
36 in +	Dual monitors, or a screen plus real writing space.
30 in	Comfortable single monitor. The target.
27 in	Fine with a monitor arm. Tight without one.
24 in	Minimum. Needs an arm to reach a proper viewing distance.
Under 24 in	Laptop-and-notebook territory. Not a monitor desk.

6: knee clearance

Sit square to the desk. If a drawer, a crossbar, or a radiator makes you angle your legs to one side, you will twist your spine for eight hours a day.

Clear it or move the desk. This is not a gear problem and nothing you buy will solve it.

If one number is wrong, fix that one first

In order of how much damage they do: desk height, then monitor height, then monitor distance, then seat height.

A $300 chair under a desk that is two inches too tall is $300 spent on the wrong problem. Work down that list and stop when the room stops annoying you.

The thing most people buy first

A second monitor. It is almost never the right first purchase — it doubles the depth problem, doubles the glare problem, and does nothing at all for posture. Fix height, light and depth first, then add screens.