The short answer: most adults should buy a size B Aeron. Herman Miller sizes the Aeron by height and weight. Size A fits people about 4’10” to 5’4” (up to 300 lb), size B fits 5’2” to 6’0” (up to 350 lb), and size C fits 5’10” to 6’6” (up to 400 lb). If you fall in an overlap, from 5’2” to 5’4” or from 5’10” to 6’0”, Herman Miller recommends size B.
The size matters more on an Aeron than on most chairs because the seat depth isn’t adjustable. Each size has its own seat, back and frame, and you can’t change the seat depth after you buy.
Aeron Size Chart
| Size A (small) | Size B (medium) | Size C (large) | |
|---|---|---|---|
| Recommended height | 4’10” to 5’4” | 5’2” to 6’0” | 5’10” to 6’6” |
| Maximum user weight | 300 lb | 350 lb | 400 lb |
| Seat height (store figures) | 14.75 to 19 in. | 16 to 20.5 in. | 16 to 20.5 in. |
| Seat depth (fixed) | 16 in. | 17 in. | 18.5 in. |
| Overall height | 38.5 in. | 41 in. | 43 in. |
| Overall width | 25.75 in. | 27 in. | 28.25 in. |
| Fixed-arm height above seat | 7.8 in. | 8.5 in. | 8.5 in. |
| Chair weight | 40 lb | 41 lb | 43 lb |
Heights, weights and dimensions are from Herman Miller’s Aeron buying guide and store listing. Herman Miller’s spec sheet lists a wider seat height range for sizes B and C (up to 22.8 inches) with the taller cylinder option, so check the cylinder on the listing if you’re tall or sit at a high desk.
Herman Miller says the three sizes cover the 1st to 99th percentile of adult body sizes, a wider range than most one-size chairs, which typically aim at the 5th to 95th.
Which Aeron Size Should You Get?
| If you are… | Buy | Why |
|---|---|---|
| Under 5’2” | A | The shorter seat stops the front edge pressing behind your knees |
| 5’2” to 5’4” | B (or A if you’re slim and short-legged) | Herman Miller recommends B in the A/B overlap |
| 5’4” to 5’10” | B | The middle of B’s range |
| 5’10” to 6’0” | B, or C if you’re heavier or long-legged | Herman Miller recommends B in the B/C overlap |
| Over 6’0” | C | Deeper 18.5-inch seat and a taller back |
| Over 350 lb | C | The only size rated to 400 lb |
Weight changes the answer as well as height. Herman Miller’s full size chart plots height against weight, and it pushes heavier people up a size because a wider body needs more room between the seat frame rails. Someone 5’6” and over about 260 lb lands in size C on that chart, not B. If the frame edges of the seat press into the outside of your thighs, you need the next size up.
What Changes Between the Sizes
Seat depth
This is the main difference: about 16, 17 and 18.5 inches for A, B and C. Most ergonomic guidance says you want two to four fingers of space between the front edge of the seat and the back of your knees. Too deep and you slide forward or perch on the edge. Too shallow and your thighs aren’t supported. Other high-end chairs, such as the Steelcase Leap and the Herman Miller Embody, use one frame with a sliding seat instead.
Seat width and frame
Each size is wider than the last (25.75, 27 and 28.25 inches overall). The Aeron’s seat is a mesh panel stretched across a rigid plastic frame, so the frame edge is where a too-small Aeron hurts first.
Back height
The back gets taller with each size (38.5, 41 and 43 inches overall), which moves the lumbar support and the top of the backrest up for taller sitters.
Seat height
Size A goes lower, down to 14.75 inches, which is why it’s the pick for people under about 5’2” whose feet otherwise dangle. Sizes B and C share the same standard seat height range of 16 to 20.5 inches. See our office chair seat height ranges for how that compares with other chairs.
Weight limit
Herman Miller tests and warrants the sizes to 300, 350 and 400 lb. Our guide to office chair weight limits compares that with other chairs.
Signs Your Aeron Is the Wrong Size
Too small:
- The seat frame edges press into the sides or backs of your thighs.
- Your thighs extend well past the front of the seat.
- The lumbar support sits too low, closer to your hips than your lower back.
Too big:
- The front edge of the seat presses behind your knees when you sit all the way back.
- Your feet don’t rest flat on the floor at the lowest seat height.
- The seat is wide enough that you can’t use both armrests without reaching outward.
How to Check the Size of a Used Aeron
Every Aeron has a manufacturing label under the seat with the product number, order number and manufacture date. On Aerons, the product number starts with AER1 followed by the size letter, so a size B chair’s number begins AER1B. If a seller can’t show the label, measure the seat depth from the front edge to the back of the seat: about 16 inches is an A, 17 a B and 18.5 a C.
Older Aerons made from 1994 to 2016, the Aeron Classic, used the same A, B and C sizes, but the Classic was rated to 300 lb in every size. Our Aeron Classic vs. Remastered guide shows how to tell them apart, and are refurbished Herman Miller chairs worth it covers buying one secondhand.
Price by Size
Size doesn’t change the price much. On Herman Miller’s store, a size B Graphite Aeron with PostureFit SL, the tilt limiter with seat angle and fully adjustable arms lists for about $2,305, and $1,613.50 in Herman Miller’s Black Friday sale (30% off in-stock chairs through November 18, 2026, and 25% off everything through December 7). The same configuration in A or C is within about $100. Herman Miller’s refurbished Aeron is $945 in all three sizes.
Sizes A, B and C
Herman Miller Aeron
Three sizes rated to 300, 350 and 400 lb, 8Z Pellicle mesh and a 12-year warranty.
Buy new from Herman Miller or an authorized dealer if you want the warranty. Herman Miller’s 12-year warranty covers only the original buyer of a new chair from Herman Miller or an authorized reseller. Herman Miller’s store also takes returns within 30 days, which is useful if you’re between sizes (a $99 return shipping fee applies). For more on the chair itself, read our Herman Miller Aeron review.
Herman Miller Aeron Size FAQ
What size Aeron should I get if I’m 5’10”?
Size B for most people. At 5’10” you’re in the overlap between B (5’2” to 6’0”) and C (5’10” to 6’6”), and Herman Miller recommends B for anyone in an overlap. Choose C if you’re heavier, have long thighs, or find B’s 17-inch seat too shallow.
What size Aeron should I get if I’m 6 feet tall?
Size B or C. Six feet is the top of B’s range and inside C’s. C has a deeper 18.5-inch seat, a taller back and a 400 lb rating. If you have long legs or weigh more than about 250 lb, C is the safer choice.
What size Aeron for a 5’4” person?
Size B for most people, or A if you’re slim and have short legs. A goes lower (14.75 inches) and has a 16-inch seat, which helps if B’s seat presses behind your knees.
Is Aeron size B the most common?
Yes. Size B is the default on Herman Miller’s store and covers the widest range of people, 5’2” to 6’0” and up to 350 lb. Herman Miller recommends it for anyone who falls between two sizes.
Can you adjust the seat depth on an Aeron?
No. The Aeron’s seat depth is fixed for each size: about 16, 17 and 18.5 inches for A, B and C. That’s why choosing the right size matters.
What is the weight limit of each Aeron size?
Size A is rated to 300 lb, size B to 350 lb and size C to 400 lb. The older Aeron Classic was rated to 300 lb in all sizes.
How do I tell what size my Aeron is?
Look at the label under the seat. The product number starts with AER1 followed by A, B or C. You can also measure the seat depth: about 16 inches for A, 17 for B and 18.5 for C.
