There is no universal clearance number
The gap a mount needs depends on its base, joints, installation method, and intended screen position. Giving every arm the same clearance allowance would conceal the dimension that matters most for a desk against a wall.
Split the problem into installation clearance and operating clearance. Can the clamp be placed and tightened? After it is installed, can the arm move to your preferred position without the joint or a cable pressing against the wall?
Read the drawing in the folded position
Maximum reach is easy to spot in a product description. Folded depth is more relevant when you want the screen close to the rear edge. Look for a side-view drawing and the arm's pivot positions. If the drawing does not provide the necessary dimension, ask the manufacturer for it.
Use a top-down paper sketch to try an offset mounting point. An arm mounted to one side might allow a joint to fold sideways, but that depends on the joint's actual range and the load restrictions. A sketch identifies a question; it does not confirm a configuration.
Allow for the small obstructions
Rear-facing video connectors, a thick power plug, blinds, a skirting board, and a wall shelf can each change the arrangement. Include them in your measurement rather than checking only the bare desk.
If an arm would force the desk far into the room, compare the complete result with the original stand. The extra free desktop may not be worth the lost floor space. Save your dimensions alongside the model number so a later replacement can be checked against the same constraints.
About this guide
Worked examples are illustrative calculations, not measurements from product testing. Follow the instructions for your exact equipment. Read our research and correction policy.