The Herman Miller Aeron is one of the most ergonomically intelligent office chairs ever made. It is also one of the easiest to get wrong. Buy the wrong size and you will spend your days sitting in a chair that digs into the backs of your thighs, fails to support your lower back, or simply feels awkward in ways you cannot quite put your finger on. Get the size right and the Aeron becomes almost invisible — it just works.
At The Good Chairs, sizing questions are the ones we get asked most. This guide covers everything you need to make the right call, whether you are buying new or pre-owned.
Why size matters more on the Aeron than on most chairs
Most office chairs are one-size-fits-all with a height adjustment lever and little else. The Aeron is different. Each size — A, B, and C — has a completely different seat pan width and depth, backrest height, and overall frame geometry. These are not minor variations. The seat pan on a size C is meaningfully wider and deeper than on a size A, and the backrest is taller. When you sit in the wrong size, the rigid plastic frame of the seat pan can press into your thighs, the lumbar support hits the wrong point on your spine, and the armrests never quite align. No amount of adjustment will fix a fundamental size mismatch.
The three sizes at a glance
Size A is the smallest configuration, measuring approximately 98 cm tall, 66 cm wide, and 41 cm deep. It is designed for smaller frames — best suited to people between approximately 142 cm and 175 cm tall, weighing between 40 and 73 kg. In practice, size A suits petite adults and those with a smaller build who would find the size B seat pan too wide, causing the frame edges to press against their outer thighs.
Size B is the most inclusive configuration, measuring approximately 104 cm tall, 69 cm wide, and 43 cm deep. It can accommodate a very wide range of bodies — from under 152 cm to nearly 213 cm tall, across a broad weight range up to 159 kg. This is why size B accounts for the vast majority of Aeron sales globally. Its engineering is specifically designed to accommodate a wide range of body types comfortably, making it the most commonly selected size in the corporate world.
Size C has the largest footprint, at approximately 109 cm tall, 72 cm wide, and 47 cm deep. It is most appropriate for taller users at the higher end of the weight range, with the same maximum weight capacity as size B at 159 kg. The taller backrest provides upper back support that taller users will not get from a size B, and the wider, deeper seat pan gives larger frames the room they need without pressure from the frame edges.
Height and weight: the starting point, not the whole answer
Herman Miller's official sizing chart cross-references height and weight to give a recommended size. It is a useful starting point, but it has limits. If you weigh 61 kg and stand 150 cm tall, size B may not be the best fit despite your weight — size A would be more appropriate, demonstrating the need to take both measurements into account together rather than independently.
As a practical guide in metric:
Size A is generally right for people up to roughly 155 cm tall and 60 kg. Size B suits the majority of people from around 155 cm to 188 cm across a broad weight range. Size C is the better choice for people over approximately 185 cm or those with a larger, broader frame who find the size B seat pan feels snug.
Where your height and weight measurements land in an overlapping zone between two sizes — A/B or B/C — Herman Miller recommends defaulting to size B, as it is designed to fit the broadest range of people. At The Good Chairs we generally agree, with one caveat: if you are at the upper end of the B/C overlap and you spend six or more hours a day in the chair, the additional seat depth and backrest height of the C will likely serve you better over time.
The measurement the chart misses: seat depth and thigh length
Height and weight tell most of the story, but not all of it. The dimension that catches people out most often is seat depth relative to thigh length. The correct seat depth for any chair is one where you can sit with your back fully against the backrest and still fit two to three fingers between the front edge of the seat pan and the back of your knee. If the seat is too deep, you will either perch forward — losing all lumbar support — or find the edge cutting into the backs of your legs.
Size B has a seat depth of approximately 43 cm, while size C sits at around 47 cm. If you have shorter legs relative to your overall height or weight, this is worth factoring in — some people who fall into the size C range by weight actually sit more comfortably in a size B due to shorter thigh length.
How to identify the size of a pre-owned Aeron
This is the single most important thing to check when buying pre-owned. The easiest method is to feel under the top lip of the backrest frame, directly behind the Herman Miller logo. One bump indicates size A, two bumps indicate size B, and three bumps arranged in a triangle indicate size C. You can also check the label on the underside of the seat, which will state the size directly on most models.
Do not rely on visual assessment alone — size A and B look very similar in photographs, and many pre-owned listings do not specify the size correctly, or at all. Always confirm before purchasing.
Classic vs Remastered: does sizing differ?
No. Both the Classic Aeron (manufactured before October 2016) and the Remastered Aeron use the same A, B, and C sizing system. The ergonomic adjustments differ slightly between generations, but the overall dimensions remain consistent. If you know your size from a Classic model you have used previously, the same size applies to the Remastered version.
What if you are between sizes?
If your measurements place you squarely in an overlap zone, the most reliable approach is to try both sizes in person if at all possible. At The Good Chairs we are happy to advise based on your specific measurements — reach out before you commit and we will point you toward the right chair.
When trying a chair, the three checks that matter most are: can you sit with your full back against the backrest without the seat edge pressing into your thighs; does the lumbar support or PostureFit SL make contact with your lower back in a natural seated position; and do the armrests reach a comfortable height when your shoulders are relaxed. If all three are right, the size is right.
A note on corporate and bulk orders
For businesses ordering multiple chairs, sizing across a team requires some thought. The most practical approach is to identify the two or three most common body types among your team and stock accordingly — typically a mix of size B and size C, with size A for any team members who fall into the smaller range. At The Good Chairs we work with corporate buyers on fit-out orders and can advise on the right split for your team. Get in touch to discuss.