Nearly every desk accessory that gets returned is returned for the same reason: it did not fit. Not because it was badly made — because a measurement nobody took turned out to matter.
Four numbers prevent almost all of it. Take them once, write them down, and buying anything for that desk becomes straightforward.
1. Usable depth
Not the depth of the desk. The depth you can actually use.
Measure from the front edge to whatever stops you at the back — a wall, a monitor stand, a radiator, a run of cables. That figure decides whether a riser can sit behind your keyboard without pushing the monitor into the wall, and whether a desk pad will lie flat rather than curling up at the back.
Most home desks are 60 to 75cm deep and have noticeably less usable depth than that once a monitor is on them.
2. Edge thickness
This is the one people skip, and it is the one that decides whether anything clamp-on will work at all.
Measure the thickness of the desktop at the edge where the clamp will go, not in the middle. Many desks have a thicker edge banding or a bevelled profile, and a clamp rated to 4cm will not close on a 5cm edge.
While you are there, check what is directly underneath that edge. A cross-brace, a drawer runner or an apron will block a clamp even when the thickness is right.
3. Clear width
Measure the horizontal run that is genuinely free — between a wall and a set of drawers, or between two monitor arms.
This decides riser span and shelf length. If you run two monitors, measure the full width both panels occupy at the spacing you actually use, then add a few centimetres. A riser exactly as wide as two monitors looks cramped and leaves nowhere for the edge of either stand.
4. Under-desk clearance
For anything that mounts underneath — drawers, cable trays, keyboard trays — measure from the underside of the desktop down to the highest thing that would collide with it. Usually that is your knees, sometimes a drawer unit, occasionally the desk’s own frame.
Then sit down and check it in the position you actually sit in, not upright and formal. An under-desk drawer that clears your knees in theory and catches them in practice gets removed within a week.
A note on sit-stand desks
Take every measurement at the height you use most, then check the extremes. The frame geometry of a moving desk changes what is reachable and what collides. Anything mounted underneath also needs to clear the mechanism through the full travel, not just at one height.
Write them down
Four numbers — usable depth, edge thickness, clear width, under-desk clearance — on a note in your phone. Every future purchase for that desk takes thirty seconds to check instead of a fortnight to return.
If you have the numbers and still are not sure which option fits, send them to us and we will tell you, including when the answer is that none of them do.