Aeron size A, B or C — what Herman Miller actually publishes, and what it does not

The last question before the cart

Everything else about this chair has been argued for thirty years — the mesh, the posture, the price. The question that actually stops a purchase is smaller and duller: am I an A, a B, or a C? Get it wrong and the warranty does not help you, because a chair that fits badly is not a defective chair.

The chair record put the warning plainly: the Aeron comes in three fixed sizes and does not become a size C by turning a knob. This record is the follow-through — what the maker publishes to answer the size question, quoted rather than paraphrased.

What Herman Miller publishes

A short PDF called the Size/Fit Reference, February 2026 edition, written for the exact case this article exists for: “This reference helps people select A-, B-, or C-size chairs when the three sizes are not available for actual test sitting.”

Three numbers in it carry a warranty behind them: “Aeron A-Size chairs are tested and warrantied for individuals weighing up to 300 pounds. B-Size chairs are warrantied for use up to 350 pounds, and C-Size chairs are tested and warrantied to support up to 400 pounds.”

And one instruction settles most boundary cases: “Since the B-size chair is designed to fit a broad range of people, Herman Miller recommends it for users who fall in the A/B or B/C category.”

One condition worth carrying: the sheet says the chart “applies to Aeron chairs with the extended-height-range pneumatic height-adjustment cylinder” — so a chair with a different cylinder is outside what this document answers.

What it does not publish

Search this question and you will be given confident body-height ranges for each size — the A for 4’10” to 5’4”, and so on down the list. We went looking for those ranges in the maker’s own sheet. They are not in its text. What the sheet gives instead is the weight limits above, and then a chart: “To determine which chair size is best, find the point of intersection for your height and weight.”

That chart is a graphic. We can link it, and we do; we cannot quote it, so we will not transcribe it into a table and present the result as Herman Miller’s numbers. The ranges circulating elsewhere may well be accurate readings of that graphic — but they arrive on pages that also sell the chair, and this library’s whole method is to say which numbers came with a signature and which did not.

How to use the three numbers

Start with weight, because it is the number the warranty is written against. Under 300 lb and the A is warranted for you; up to 350 the B; up to 400 the C. Above 400, the Aeron is not the chair, and the chair record’s alternative — a Leap V2 Plus rated to 500 lb — is.

Then read the chart in the maker’s PDF for the height axis. If it puts you between two sizes, you already have the maker’s answer: take the B. That single sentence resolves the majority of real cases, because the B is the size Herman Miller built to be forgiving.

And if you can sit in all three, do that instead. The maker’s own document exists because you often cannot — it is a substitute for the showroom, and it says so in its first line. A chair meant to last a decade is worth twenty minutes in a shop, and no chart replaces the twenty minutes.

Where the Aeron’s twelve-year warranty sits against the other serious maker in this category — including which parts each one covers — is read page against page in Herman Miller vs Okamura.