Aeron size A, B, or C: how to pick without a showroom trip
The Aeron is not sold in one size — it's sold in three, and the difference is structural, not just fabric. The frame, seat depth, and mesh tension are all engineered for a specific body range. Wrong size = none of the ergonomic benefits the chair is famous for. The good news: for ~90% of adults, there's one obvious answer. Here's how to figure out which one is yours.
The three sizes at a glance
| Size | Height range | Weight range | Seat width × depth |
|---|---|---|---|
| A (small) | 4'10" – 5'4" | 95–140 lbs | 25.75" × 15" |
| B (medium) | 5'2" – 6'6" | 130–230 lbs | 27" × 16.75" |
| C (large) | 5'11" – 6'8" | 200–300 lbs | 28.25" × 18.5" |
The single biggest variable: your thigh length
Height and weight will get you in the ballpark. The decisive measurement is your thigh length — from the crease behind your knee to the crease at your hip, seated. This determines whether the seat pan supports you correctly. Too long and the seat cuts into the back of your knees (nerve compression, numbness in your feet). Too short and you lose thigh support (back of thigh hovers, hip flexors tense up). Use a tape measure on a hard chair: sit flat, measure back-of-knee to front-of-butt.
- Thigh length 16" or less → Size A.
- Thigh length 17"–19" → Size B.
- Thigh length 19" or more → Size C.
Why Size B is 85% of the market
If you're a 5'4" to 6'2" adult weighing 130–230 lbs, you are Size B. This covers the vast majority of working-age adults. Herman Miller produces more Size B units than A and C combined, which is why used/open-box Size B inventory is easy to find and Size A/C inventory is scarcer.
When to size down (or up)
Edge cases happen. If you're on the tall end of Size A's height range (5'4") but you have short thighs, go A, not B — thigh length wins over height. If you're 5'11" and weigh 240 lbs, the ranges overlap between B and C; you'll be more comfortable in C. If you're 6'3" and 180 lbs, you're on the upper end of B's height range but your thighs probably aren't long enough to warrant C. If you're unsure, lean toward the smaller size — an Aeron slightly too small is more forgiving than one slightly too large.
What doesn't matter
- Frame color (Graphite, Carbon, Mineral). Cosmetic. No ergonomic difference.
- Mesh color (Graphite, Carbon, Mineral, etc.). Cosmetic.
- Year of manufacture past 2016 (the 'Remastered' redesign). The Remastered Aeron is what you want; earlier 'Classic' Aerons are a different design with older lumbar.
- Fully Loaded vs standard adjustments. Fully Loaded gets you forward tilt and adjustable arms — both useful but not required. The core ergonomics are the same.
PostureFit SL vs PostureFit
All modern Aerons ship with some form of lumbar support. Standard lumbar is a pad that presses into the small of your back. PostureFit SL is an upgraded lumbar — two pads, upper and lower — that supports the sacrum and lumbar spine independently. If you have lower-back pain, PostureFit SL is the spec you want. We tag chairs with PostureFit SL as 'PF' in the listing.
Final decision
- Measure your height, weight, and thigh length.
- Pick the size that matches all three (usually B).
- Check the inventory below for what's in stock in that size.
- Pick PostureFit SL if you have back pain; standard lumbar is fine otherwise.
Common questions.
- What Aeron size am I if I'm 5'10" and 180 lbs?
- Size B. That's the center of the B range on both height and weight. Size B will be the right call for more than 90% of adults between 5'2" and 6'2".
- Can I resize the chair after I buy it?
- No. The three sizes are structurally different — the frame, seat pan, and mesh are all dimensioned for a specific body range. The seat-depth adjustment (on some versions) moves the pan forward or back a few inches but does not change the underlying size.
- What if I'm on the boundary between two sizes?
- Use thigh length as the tiebreaker. If you measure 16" or shorter, go A. 17–19", go B. 19" or longer, go C. When still unsure, size down — a slightly small Aeron is more forgiving than a slightly large one.
- Is there a Size D?
- No. Herman Miller does not make a Size D Aeron. For people over 300 lbs or taller than 6'8", the Herman Miller Embody or Steelcase Leap Plus are better options.
- Does the size affect the price?
- Slightly. Sizes A and C are less common in the used market than B, so they occasionally trade at a small premium when demand meets thin supply. On our site, price reflects the specific unit's condition, not just its size.