The Herman Miller Aeron comes in three sizes: A (small) for 4 ft 10 in to 5 ft 4 in and up to 300 lb, B (medium) for 5 ft 2 in to 6 ft and up to 350 lb, and C (large) for 5 ft 10 in to 6 ft 6 in and up to 400 lb. Seat depth is 16, 17 and 18.5 in, and when you fall between two sizes, Herman Miller’s buying guide says take B.
The letter is permanent. Size sets seat depth, seat width, back height and the rated user weight together, and the Aeron has no seat-depth slider to rescue a wrong pick. Herman Miller’s height-by-weight fit chart is decoded below, with the full dimensions behind it and the cases where “B fits most people” is the wrong advice.
Aeron size chart: A, B and C at a glance
| Size | User height | Max user weight | Seat depth | Seat height, standard cylinder | Chair weight |
|---|---|---|---|---|---|
| A (small) | 4 ft 10 in to 5 ft 4 in (147-163 cm) | 300 lb (136 kg) | 16 in (41 cm) | 14.75-19 in (37.5-48 cm) | 40 lb |
| B (medium) | 5 ft 2 in to 6 ft 0 in (157-183 cm) | 350 lb (159 kg) | 17 in (43 cm) | 16-20.5 in (41-52 cm) | 41 lb |
| C (large) | 5 ft 10 in to 6 ft 6 in (178-198 cm) | 400 lb (181 kg) | 18.5 in (47 cm) | 16-20.5 in (41-52 cm) | 43 lb |
Heights, weight caps, seat heights and chair weights are from the Herman Miller store listing; seat depths are from the Aeron spec page. The bands overlap at 5 ft 2 in to 5 ft 4 in (A or B) and 5 ft 10 in to 6 ft (B or C), and the buying guide sends both overlaps to B, the size “designed to fit a broad range of people.” Weight overrides height: past 300 lb A is out, and past 350 lb only C remains. Herman Miller’s other models are covered in our Herman Miller chair sizes guide.
Who each size is for
Size A (small)
Under about 5 ft 2 in and under about 130 lb is the only zone where the chart says A outright. The pain pattern A solves is a pan that is too deep: pressure behind the knees, or sliding forward off the lumbar support to get your feet flat. A is also the only size whose standard cylinder drops below 16 in, to 14.75 in.
Size B (medium)
The middle of the population and Herman Miller’s default whenever you land on a boundary. Between 5 ft 3 in and 6 ft 4 in, B appears on the chart somewhere up to about 250 lb, or about 270 lb from 5 ft 11 in up. The store’s FAQ calls it the most commonly selected size.
Size C (large)
Tall, heavy or both. Outright C starts at 200 lb for anyone 6 ft 5 in and over, and at 260 to 280 lb from 5 ft 3 in upward. It is also the only size rated to 400 lb in current documents. The pain pattern it solves is hip pressure against the hard frame edge of a B, and a pan too short to carry the thigh.
If existing back, hip or leg pain is the reason you are shopping, get a diagnosis before a chair. A chair fits a body; it does not treat one.
Aeron chair dimensions by size
| Size A | Size B | Size C | |
|---|---|---|---|
| Overall height | 34.2-38.5 in (87-98 cm) | 36.8-41.1 in (93-104 cm) | 40-45.4 in (102-115 cm) |
| Overall width, armless, fixed or height-adjustable arms | 27.5 in (70 cm) | 28.3 in (72 cm) | 28.3 in (72 cm) |
| Overall width, fully adjustable arms | up to 29.3 in (74 cm) | up to 30.4 in (77 cm) | up to 31.6 in (80 cm) |
| Overall depth | 27-27.5 in (69-70 cm) | 27.5-28.3 in (70-72 cm) | 27.5-28.3 in (70-72 cm) |
| Seat depth, spec page / product sheet | 16 / 16.4 in (41 / 42 cm) | 17 in (43 cm) | 18.5 / 18.9 in (47 / 48 cm) |
| Seat height, all cylinders | 14.4-19.3 in (37-49 cm) | 14.8-22.8 in (38-58 cm) | 15.8-22.8 in (40-58 cm) |
| Fixed arm height above seat | 7.8 in | 8.5 in | 8.5 in |
| Gap between armrests (approx.) | 17 in | 18.5 in | 20.5 in |
| Seat frame width, Classic Aeron | 19 in | 20.3 in | 21.5 in |
Overall dimensions, spec-page seat depths and all-cylinder seat heights are from Herman Miller’s spec page; the second depth figure is from the product sheet; fixed arm heights are from the buying guide, though the spec page prints 8.5 in for A as well. The armrest gap is Crandall’s figure for classic-era chairs, and the seat frame widths come from a Classic Aeron replacement-seat listing.
Herman Miller’s documents disagree by fractions of an inch. The product sheet prints 38.5, 41.1 and 43 in tall and 25.8, 27 and 29.3 in wide; the store prints 38.5, 41 and 43 in tall, 25.75, 27 and 28.25 in wide, and B’s depth as 16.75 in. The split that matters is seat depth: the product sheet runs 0.4 in deeper on A and C, so the step from B to C is 1.5 or 1.9 in depending on the document.
The row to stare at is seat depth. OSHA’s workstation guidance asks for a pan that supports the thigh without contacting the back of the knee, and expects depth to be adjustable so tall and short users can both sit fully back. On the Aeron, depth adjusts only in the sense that you choose A, B or C on the order form. After that it is fixed.
Aeron specs that are the same on every size
Arm travel, tilt options, PostureFit SL and the warranty are identical across sizes. From the spec page, store listing and buying guide:
- Tilt. Harmonic 2 tilt with a tension knob under the front of the seat. Options add a tilt limiter (upright, mid-recline or full recline) and a seat angle adjustment from horizontal to 5 degrees forward.
- Back support. PostureFit SL (two pads, one for the lumbar and one for the sacrum), an adjustable lumbar pad with 4.5 in of vertical travel, or basic back support. Setup is in how to adjust lumbar support.
- Arms. About 4 in of height travel on every size: 7.5 to 11.5 in above the seat on the spec page, 6.8 to 10.8 in in the buying guide. Fully adjustable arms also slide 2.5 in forward and back.
- Casters and base. Carpet or multi-surface casters, both 2.5 in in diameter, on a 26.5 in base.
- Suspension. 8Z Pellicle mesh; mesh versus foam covers the heat and wear trade-offs.
- Warranty. 12 years, rated for three shifts.
In October 2026 the store showed $2,305 for its default configuration and listed configurations including a size C at $2,045 and a size A at $2,575. Options set the price; the size letter is a fit decision, not a price tier.
The official fit chart, decoded
Herman Miller’s Size/Fit Reference (February 2026 edition) is a grid of height against weight, shaded into five zones. Read row by row, in pounds:
| Height | A only | A or B | B | B or C | C only |
|---|---|---|---|---|---|
| 4 ft 8 in to 4 ft 11 in | 90-120 | 130-160 | 170-290 | 300-320 | 330+ |
| 5 ft 0 in to 5 ft 1 in | 90-120 | 130-160 | 170-210 | 220-320 | 330+ |
| 5 ft 2 in | 90-160 | 170-210 | 220-270 | 280+ | |
| 5 ft 3 in to 5 ft 9 in | 90-160 | about 170 | 180-250 | 260+ | |
| 5 ft 10 in | 90-170 | 180-250 | 260+ | ||
| 5 ft 11 in to 6 ft 4 in | 90-150 | 160-270 | 280+ | ||
| 6 ft 5 in to 6 ft 7 in | 90-150 | 160-190 | 200+ |
The grid is drawn in 10 lb cells, so treat every boundary as plus or minus one cell. Three things fall out of it that the store’s simple height bands hide. Weight decides the top end: a 4 ft 8 in sitter at 330 lb is a C, full stop. Tall and light is a B: at 6 ft 7 in and 150 lb the chart never suggests C. And the A-or-B overlap is wide, covering the whole 90 to 160 lb range from 5 ft 3 in to 5 ft 9 in, which is where most of the confusion lives. The chart’s own footnote says it applies to chairs with the extended-height cylinder; on a standard cylinder the B and C seat-height floor is 16 in, not 14.8.
What size Aeron chair do I need?
Size B, unless your height or weight pushes you out of it. The fit chart puts you in A outright only under about 5 ft 2 in and under about 130 lb, and in C outright from 260 to 280 lb between 5 ft 2 in and 6 ft 4 in, or from 200 lb at 6 ft 5 in and taller. Everyone else lands on B or a B overlap, where Herman Miller says take B. To confirm:
- Height band. A covers 4 ft 10 in to 5 ft 4 in, B 5 ft 2 in to 6 ft, C 5 ft 10 in to 6 ft 6 in. One band only is your provisional size.
- Weight. Over 300 lb rules out A; over 350 lb leaves only C. The grid moves people to C earlier, from 260 lb at 5 ft 3 in to 5 ft 10 in.
- Grid cell. “A only”, “B” or “C only” settles it; an overlap cell means keep going.
- Thigh length. Buttock to the back of the knee against the 16, 17 or 18.5 in pan, leaving 1 to 2 in behind the knee.
- Seat height. If your feet do not reach the floor at 16 in, B and C need a footrest; A goes down to 14.75 in.
- Hips. Compare hip width with the armrest gap, then recheck knee clearance before sizing up.
Between sizes: what to measure
Herman Miller’s stated rule, repeated in its buying guide, is to take B in either overlap zone. Treat that as a starting point, then check thigh length and hip clearance while seated.
Short thighs first. Sit on a flat bench with your back against a wall and measure from the wall to the crease behind your knee. At 17.5 in, a B pan (17 in) leaves only 0.5 in of nominal clearance; compare A’s 16 to 16.4 in pan and check the actual gap while sitting fully back. Wide hips second. Check clearance against the rigid seat frame as well as the armrests, but do not size up for width without checking knee clearance again.
A 19 in buttock-to-knee measurement suggests roughly 17-18 in of usable seat depth as a starting point, allowing 1-2 in of clearance before a seated fit check. B’s listed 17 in depth leaves about 2 in on paper; C’s 18.5 to 18.9 in leaves 0.1 to 0.5 in. That measurement alone does not justify choosing C. Use the seat-depth measurement guide to check usable depth with your back supported and no pressure behind the knees, as OSHA’s guidance requires, then check width, height range and weight rating.
Seat height, cylinders and the desk
Size A tops out at 19.3 in even on the extended cylinder. Against a fixed 29 in desk that leaves a short sitter with elbows below the keyboard and nothing to fix on the chair side; the fix is a lower desk or a footrest. B and C on the standard cylinder start at 16 in, which is high for anyone under about 5 ft 4 in who wants feet flat, and another reason the A-or-B zone deserves a measurement rather than a default. The ergonomic chair and desk sizer on this site turns your height into a target seat height to check against those ranges.
The 350 lb versus 400 lb question
Current Herman Miller documents rate size C to 400 lb. Older listings, BTOD’s 2026 review and remanufacturers such as Crandall still quote 350 lb for C. The difference tracks the chair’s generation: the lower figure belongs to classic-era stock. If a rating above 350 lb is the reason you are buying a C, buy current production and keep the receipt, because the warranty is written around normal use and the rating on the chair you own is the one that counts.
How to tell which Aeron size you have
Every Aeron carries raised dots under the top edge of the back frame, opposite the Herman Miller logo: one dot for A, two for B, three for C. Aeron Chair Parts adds that the B dots sit side by side and the C dots form a triangle, and gives a second check: the tag under the seat carries a model number starting with AE, and the letter after the W is the size. On a Classic chair, the seat frame widths in the table above are a rough third check. Feel for the dots before paying for a used chair, since listings routinely get the letter wrong.
Wear and warranty
The MillerKnoll warranty effective March 15, 2026 covers the Aeron for 12 years, parts and labor, regardless of how many shifts a day it is used. Herman Miller’s materials schedule lists 8Z Pellicle mesh and leather under 12-year coverage. Check the warranty terms applicable to your purchase date and keep proof of purchase; normal wear and tear is excluded. Nothing in the warranty varies by size.
Compared to
Steelcase Leap. One size, and the pan slides: Steelcase’s specification guide lists a functional seat depth of 15.75 to 18.75 in, with a 400 lb rating and a 12-year multi-shift warranty. If you sit on an Aeron size boundary, the Leap removes the risk.
The Aeron one size over. C’s pan is 1.5 to 1.9 in deeper than B’s, depending on which Herman Miller document you read, and its armrest gap about 2 in wider. Consider it only after checking both width and usable depth, along with seat height and weight rating. The chart’s overlap zone is a reason to compare sizes, not to skip knee clearance.
Related across the network
- Best Ergonomic Chair for Long Hours: What the Specs Tell You (ergoranker.com)
Related on this site
FAQ
can a 6 foot person use an aeron size b
Yes. Herman Miller’s store recommends size B for people 5 ft 2 in to 6 ft, and its fit grid keeps B as an option up to 6 ft 4 in for anyone up to about 270 lb. From about 160 lb at that height you are in the B-or-C zone, where thigh length should decide.
what are the dimensions of the aeron size b
Aeron size B has a 17 in (43 cm) seat depth and a 14.8 to 22.8 in seat height across cylinders, or 16 to 20.5 in on the standard cylinder. Herman Miller’s spec page lists it at 36.8 to 41.1 in tall and 28.3 in wide without arms. It is rated to 350 lb and weighs 41 lb.
what is the weight limit on an aeron chair
Current Herman Miller documents rate size A to 300 lb (136 kg), size B to 350 lb (159 kg) and size C to 400 lb (181 kg). Resellers such as Crandall and BTOD still quote 350 lb for classic-era size C chairs, so check which generation you are buying before relying on the 400 lb figure.
does aeron size c sit higher than size b
No. On the standard cylinder, sizes B and C share the same 16 to 20.5 in seat height, and across all cylinder options both top out at 22.8 in; C’s floor is actually 1 in higher, at 15.8 in. Moving up to C buys a deeper pan, a taller back and a 400 lb rating, not seat height.
how wide is an aeron chair
Herman Miller’s spec page lists the Aeron at 27.5 in wide for size A and 28.3 in for sizes B and C, or up to 29.3, 30.4 and 31.6 in with fully adjustable arms. The store prints narrower figures of 25.75, 27 and 28.25 in. Between the armrests, a reseller measures roughly 17, 18.5 and 20.5 in.
