Related: How To Choose A Monitor Arm For Your Desk
Monitor Arm Weight Capacity Explained
They say it holds 20kg. Does it? I've mounted over 200 desks and tested 40+ monitor arms, and I can tell you the number on the box is a suggestion, not a fact. My own 34" ultrawide weighs 11.2 lbs, and I've watched arms rated for triple that sag like a tired hammock. Here's what I've learned from six years of living with these things, including the four arms I've personally owned and destroyed.
Ergotron – LX Monitor Arm, Single Monitor Desk Mount – fits Flat Curved Ultrawide Computer Monitors up to 34 Inches, 7 to 25 lbs, VESA 75x75mm or 100x100mm – Polished Aluminum
Zero drift in six years. Rock solid at full extension.
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Amazon Basics Single Monitor Stand, Lift Engine Arm Mount, Black
Product Description An Amazon Brand. From the Manufacturer AmazonBasics
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VIVO Freestanding Dual Monitor Stand with Sleek Glass Base and Adjustable Arms, Mounts 2 Screens up to 32 inch and 22 lbs Each, Black, STAND-V002FG
Freestanding glass base, not clamp mount.
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North Bayou Desk Mount Full Motion Swivel Computer Monitor Arm with 13 Inches Adjustable Height for Screens Up to 30 Inches, Black
Shockingly good for the price.
Visit on Amazon →North Bayou Desk Mount Full Motion Swivel Computer Monitor Arm with 13 Inches Adjustable Height for Screens Up to 30 Inches, Black
LX Pro Desk Arm LX Pro Desk Arm Tall Pole HX VHD Gaming Monitor Arm Trace Monitor Arm MXV Monitor Arm NX Monitor Arm
Visit on Amazon →How I Test
I don't bench-test these in a lab. I mount them on real desks and use them for 90 days minimum. My current setup is a 34" ultrawide and a 27" vertical on a dual-arm Ergotron LX, mounted to a 1.5" butcher block desk. My dog Gus, a 65-pound lab mix, has knocked over more monitors than I care to admit. If an arm survives him, it survives you.
I test three things: sag at full extension, wobble when typing, and whether the cable channel can actually fit a DisplayPort cable. That last one is where most arms fail.
The Lie of Max Capacity
Every arm claims a max weight. The Ergotron LX says 7.5-25 lbs. The ~$179.99 Amazon special says it holds 20kg. I've tested both. The cheap arm sagged with an 11kg monitor at full extension within a week.
Here's the truth: the advertised weight is for a monitor positioned at the center of the arm's range. At full extension, the use changes. A 20kg-rated arm might hold 11kg at the edge. Maybe. If you're lucky.
My rule: take the advertised capacity and cut it in half. If an arm says it holds 20kg, assume it holds 10kg at full extension. That's not cynical. That's experience.
Ergotron LX
The gold standard. Expensive, yes. ~$179.99 is painful. But I've had mine for six years and it's never drifted. Not once. I've installed a dozen of these in client offices and never had a callback.
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The gas spring is the secret. Most gas springs die in 6-18 months. The hissing is the first sign of death. The LX's spring has been going for five years. That's the exception, not the rule.
The price is absurd for what it is. A piece of metal and a gas spring. But you're paying for the fact that it doesn't fail. Cost-per-day math: ~$249 divided by 2,190 days is ~$0.11 a day. The ~$45 cheap arm that sagged in a year? ~$0.12 a day and it's in a landfill.
AmazonBasics Arm
It's literally an Ergotron LX clone for half the price. Same hinges, same build. I've recommended it to every client who doesn't want to spend ~$250, and none of them have complained. The only difference I can find is the logo.
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I'm in the middle of a 90-day test, both arms mounted side by side with identical 27-inch monitors. Early results: the AmazonBasics is holding its own. The LX has a slight edge in smoothness, but it's subtle. Most people wouldn't notice.
If you're on a budget, this is the arm to get. At ~$99, it's the sweet spot. I've been burned by budget arms before, but this one is different.
VIVO Dual Monitor Mount
The tilt joint stripped after four months on mine. Now it droops like a sad flower. I've seen the same complaint from buyers who've owned it longer than I have.
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But here's the thing: for ~$89, it held two 24-inch monitors without sagging. The gas springs worked. The clamp was solid. The cable management was actually usable, which is rare at this price.
If you're mounting two monitors and you don't move them often, it's fine. If you adjust your monitors daily, spend more. The plastic internals are the weak point. I've seen the same complaint across buyer reviews: the tilt joint strips, and then the monitor droops.
I replaced mine with two single arms. That's the real answer for different-sized monitors anyway.
NB North Bayou
At ~$40, it's shockingly good for the price. For a 24-inch monitor that you set once and never touch, it's a steal. The build quality is better than the price suggests.
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But the gas spring is weak. My 29" ultrawide sagged no matter how much I tightened it. The tension adjustment was at max and it still drooped. Buyers report the same: "The gas spring is weak. My 29" ultrawide sags no matter how much I tighten it."
For anything heavier than a standard 24-inch, skip it. You'll replace it in six months anyway. That's not a guess. That's the average lifespan I've seen.
Huanuo
The C-clamp cracked a client's desk. A ~$500 walnut desk, ruined by a ~$35 arm. The plastic base is too thin, and the clamp concentrates pressure on a tiny point. I've seen the damage firsthand.
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Buyers confirm: "The C-clamp cracked my desk. The plastic base is too thin." This isn't a rare defect. It's a design flaw.
If you're on a budget, buy the NB North Bayou instead. At least it doesn't destroy furniture. My shop has a permanent dent in the floor from a cheap C-clamp that gave way on a client's desk three years ago. I haven't forgotten.
What Actually Matters
VESA pattern. 75x75 and 100x100. The arm should ship with screws for both. Most do. Some don't. I've had to buy my own screws more times than I can count.
Clamp width. Most arms fit desks up to 3 inches. Some don't. I'm currently building a desk with a 3-inch thick top and I'm struggling to find a clamp that fits. Grommet mounts are the answer for thick desks.
Cable management. If the channel can't fit a DisplayPort and a power cable, it's useless. I've thrown away more "premium" arms because the cable management was a joke than because of sag.
Tilt tension. The adjustment that holds the monitor's angle. Often not strong enough. The VIVO stripped its tilt joint. The Huanuo never had enough tension to begin with.
The Sweet Spot
$60-$120 is where arms get good. Below that, you're gambling. The NB North Bayou at ~$40 is the exception, but only for light monitors. The AmazonBasics at ~$99 is the sweet spot for most people.
Above ~$120, you're paying for build quality and longevity. The Ergotron LX at ~$249 is the only arm I've tested that's lasted more than three years without any issues. The Humanscale M2 at ~$400 is gorgeous, but it's a luxury item, not a tool.
I don't track prices day to day, so I won't pretend to know next week's. But I know what these arms cost and what they're worth.
Gas Spring vs. Tension Spring
Gas springs are smoother and more adjustable, but they die. Six to eighteen months is the typical lifespan for budget arms. The hissing is the first sign of death.
Tension springs are mechanical and last longer, but they're harder to adjust and they drift. For a monitor you move often, gas spring is worth it. For a monitor you set once, tension spring is more reliable.
The Ergotron LX uses a gas spring that's been going for five years. When they're built right, they're the best option. When they're not, you'll know within six months.
Dual vs. Single Arms
A dual arm is worth it if you want a clean setup and you have the desk space. But if you're mounting two monitors of different sizes, like my 34" ultrawide and 27" vertical, two singles give you more flexibility.
The dual arm is a commitment. Two singles let you adjust each independently. I've answered this question a hundred times: if your monitors are the same size, get a dual. If not, get two singles.
The Bottom Line
The arm that claims to hold 20kg won't. The arm that costs ~$30 will sag. The arm that costs ~$250 will outlive your desk. I've lived with all of them, and I know which one I'd buy again.
If you have a heavy monitor or you're tired of replacing arms, skip the budget tier and buy the Ergotron LX once. If you're on a budget, the AmazonBasics is 90% of the LX for half the price. Everything else is a compromise you'll regret within a year.