SIHOO M18 Ergonomic Office Chair Review (Australia, 2026)

The M18 sits in the crowded mid-tier between flimsy sub-$150 task chairs and five-figure ergonomic flagship seats, and it has become the chair people recommend in that gap for one reason: it adjusts in the places that actually matter. The lumbar pad moves up and down and tilts to follow the curve of your spine, and the headrest supports the neck without shoving your head forward. Plenty of cheaper chairs have one or the other; fewer have both properly.

Add a mesh back that stays cool through a Sydney summer and an aluminium wheelbase that feels a class above the plastic bases it competes with, and you get a chair whose build quality punches above its price. That combination — real adjustability plus a solid base — is why it keeps surfacing as the mainstream ergonomic answer.

For an eight-hour day the adjustable lumbar does genuine work: rather than a fixed pillow that may or may not hit your lower back, you dial its height to where your spine actually needs support. The three-position tilt lock lets you recline and rest without the chair suddenly giving way, which is the feature people on fixed-upright chairs don't know they're missing until they try it.

The honest weak point is the seat cushion. It's thinner than what you'll find on premium-tier chairs, and owners sitting continuously past roughly six hours frequently add a memory-foam seat topper. That's a fixable comfort gap rather than a deal-breaker, but if you already know you need a plush seat, budget for the topper from day one rather than being surprised by it in week three.

The aluminium wheelbase is the detail that separates the M18 from budget rivals. Owners consistently report the gas cylinder holds its height over twelve months rather than slowly dropping — a very common failure on cheap chairs that looks fine on day one. The mesh is a taut, breathable nylon that keeps its tension well, and the castors roll cleanly on both hard floors and low-pile carpet.

Assembly is a 30-to-40-minute job with the included tools and is manageable alone. The one thing to confirm at purchase is that you're getting the current Australian revision with the padded headrest, because older stock circulated without it, and the padded version is a noticeable comfort improvement for anyone who leans back.

The armrests are three-dimensional: they adjust for height, move forward and back, and pivot inward. That covers most sitting positions and a mixed-height household sharing one chair, and forward-and-back armrest travel is genuinely useful when you switch between keyboard work and reading back in the recline.

What it lacks is inward armrest travel (four-dimensional adjustment), which is the one feature a very narrow-shouldered user might want to bring the pads snugger to their body. If that's you, look at chairs with 4D armrests in our office chair guide; for most people the 3D range here is more than adequate.

Assembly is a straightforward 30-to-40-minute job with the included tools, and most people can do it alone — you attach the castors to the wheelbase, mount the gas cylinder, bolt the mechanism into the seat pan, and fix the backrest and headrest upright. The only fiddly bit is keeping the self-tapping screws aligned while you tighten the back, which is a two-hand job if you can get a second person, but manageable solo.

Once built, spend real time dialling it in rather than accepting the out-of-box position. Set the seat so your feet are flat and thighs roughly level, adjust the lumbar height until it meets the small of your back rather than pressing your mid-back, then tune the headrest so it supports the base of your skull without shoving your head forward. Most complaints about this class of chair are really complaints about unadjusted chairs — the M18 gives you the adjustments; you have to use them.

Because the lumbar, seat height, armrests and tilt tension all adjust independently, one M18 can serve several body sizes in a household reasonably well — two people working from home on the same chair can each dial in their own setup between sessions. The tilt-tension knob is the sleeper feature here: it lets a lighter user set enough resistance that the recline doesn't slam them backward, and a heavier user set it loose enough to recline without forcing it.

The weight rating sits around 150kg, and the aluminium base is what makes that feel stable rather than flexy under load. Heavier sitters who've been uncomfortable in chairs with thin plastic mechanisms tend to report the M18 holds up better over time. If you're near the top of that range and sit for very long stretches, the thinner seat cushion becomes more noticeable, so pairing the chair with a quality seat topper is the one upgrade worth making.

Beyond the body-range limits, the recurring owner complaints for this chair are specific and worth knowing before you buy. The most common is the seat cushion thinness on long sitting days, which a topper solves cheaply. The second is the headrest range: at its highest it suits taller sitters, and people nearer the short end of the fit range find it presses the crown rather than cradling the neck — which is really the same 160cm limit showing up in practice.

A smaller but frequent note is that the armrest pads are firm rather than cushioned, so if you rest your forearms on them heavily while typing you may find them unyielding over months. None of these are build failures — they're the corners this price tier cuts to hit the number — but an owner expecting a plush, fully-padded chair out of the box will be disappointed on exactly these points where the chair is comparatively spartan.

The useful summary is that the M18 spends its budget where it matters for support and durability — the adjustable lumbar, the mesh, the aluminium base — and saves it on the softer comfort touches like cushion depth and armrest padding. For a workhorse home-office chair that prioritises posture and longevity over plushness, that's generally the right allocation.

If you're between about 160 and 190cm, working from home most days, and want one robust chair that several household members can each dial in for themselves, the M18 is the safest mainstream pick we'd recommend. It adjusts properly, it's built to last longer than the price implies, and it doesn't overpromise.

Walk away if you're shorter than about 160cm (the headrest becomes a posture problem), if you need 4D armrests or a genuinely plush seat out of the box, or if your budget stretches to a full ergonomic flagship that will comfortably out-class this at marathon sitting. And if you just need a chair for an hour or two of emails, a good task chair under $150 saves you money you won't miss.

Our bottom line: the M18 has earned its reputation by putting its money where it counts — real lumbar and headrest adjustment, a cool mesh back and a base that outlasts the plastic chairs around its price — rather than by chasing plush extras. For the broad middle of the height range doing full-time desk work, it's the least-risky ergonomic chair you can order online in Australia, and the main thing to get right is simply checking your height against its fit range before you click buy.