Should Two Monitors Share One Arm, or Should Each Get Its Own?
Summary
That depends on how you split your time between the screens. If you use both about equally, they sit side by side and meet in the middle, a symmetrical layout that one dual arm on a single post is built to hold. If one screen gets most of your attention, it goes directly in front of you and the other sits off to one side, and two single arms set that up without forcing one side of a shared arm to stretch further than the other.
Which screen do you look at most?
OSHA's evaluation checklist covers both cases in one item. "If multiple monitors are used, the position of the primary monitor is directly in front of the user and the other monitors are directly beside it. If time is split evenly between monitors, they are next to each other within a comfortable viewing angle with minimal head movement."
CCOHS describes the same two layouts in more physical terms.
- Both used equally: "Position the monitors in front of you with the edges touching," angled so the pair forms a semi-circle.
- One used more: "Place the monitor you use most directly in front of you as if it were a single monitor," with the second on one side, angled in.
In both layouts CCOHS keeps the screens about an arm's length away and at the same height. Our dual-monitor setup guide covers the rest of the desk around a pair of screens.
Deciding which case you are in takes a day of noticing. Someone who writes in one window and glances at chat or email in the other has a primary screen. Someone comparing two documents side by side, or editing across both, is closer to an even split.
How each layout sits on the hardware
In the even layout, the join between the screens lines up with your nose. A dual arm with its post behind that join holds both screens from one clamp, each side reaching the same distance.
In the primary-and-side layout, the main screen is centered on you and the second hangs off to the left or right. Around a single post, the two sides now reach different distances and angles. Two single arms, each clamped behind its own screen, place each one without borrowing reach from the other. They also handle screens of different sizes or weights more easily, since each arm can be rated for its own monitor.
Matching tops is the other detail. A 27-inch and a 24-inch screen have their centers at different heights once their top edges line up. Whichever hardware you use, each screen needs its own height adjustment.
Space along the back edge
OSHA's purchasing guide asks that when "multiple monitors are used, enough space and clearance are provided for them." Two screens are wider than they look in a listing. A 16:9 screen sold as 24 inches has a picture about 21 inches wide, so two of them edge to edge span roughly 42 inches before the frames. Two single arms also need two clamp positions along the back edge, each with the overhang and underside clearance its spec sheet asks for.
Weight reads differently on a dual arm too. Its spec sheet may give a limit for each side or one figure for the pair, and the two are easy to confuse.
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Sources
- OSHA Computer Workstations eTool, Evaluation Checklist
- OSHA Computer Workstations eTool, Purchasing Guide
- CCOHS, Office Ergonomics - Positioning the Monitor
We have not tested these products. Specs and guidance are as published on these pages on the date above and can change; the manufacturer's page for your model has the current details.