The UK Office Chair Size Guide

Choosing the wrong size office chair is one of the most common — and most fixable — ergonomic mistakes. A chair that is too large fails to support a smaller body; a chair too small creates pressure points and restricts movement regardless of its quality. This guide covers everything you need to get the size right before you order.

Why Chair Sizing Matters

An ergonomic chair can only do its job when it fits the person sitting in it. The Herman Miller Aeron — widely considered the best ergonomic chair in the world — is available in three sizes for exactly this reason. PostureFit SL and 8Z Pellicle mesh are irrelevant if the seat pan is the wrong width for your hips or the backrest doesn't reach your lumbar region. Getting the size right is the foundation everything else is built on.

Herman Miller Aeron Sizes Explained

The Aeron is the only major ergonomic chair offered in a three-size system as standard. Most chairs come in one size and rely on adjustability to accommodate a range of users. The Aeron takes a different approach: three distinct frame sizes, each with proportional seat, backrest, and mechanism dimensions.

Size	User Height	User Weight	Seat Width	Best For
Size A (Small)	Under 5'4" (163cm)	Up to 65kg (143lbs)	432mm	Smaller adults, many women
Size B (Medium)	5'3"–6'0" (160–183cm)	Up to 115kg (253lbs)	483mm	Most adults — the default choice
Size C (Large)	Over 5'10" (178cm)	Up to 159kg (350lbs)	533mm	Taller or larger adults

If you're between sizes: Size B fits the majority of adults in the UK. If you're over 6'0" or over 100kg, Size C is worth considering even if you fall within the B range — the additional seat width and backrest height provide meaningfully better support for larger frames. If you're under 5'4" and lighter, Size A will support you significantly better than a B, which will feel too wide and prevent proper lumbar contact.

General Chair Sizing: What to Measure

Seat Height Range

The most important measurement. Your ideal seat height puts your feet flat on the floor with your thighs parallel to the ground and your knees at approximately 90 degrees. Measure the distance from the floor to the back of your knee while seated — this is your ideal seat height.

• Average UK women: ~42–46cm seat height
• Average UK men: ~45–50cm seat height
• Most quality chairs: 42–52cm gas lift range — check this covers your measurement

Seat Depth

Measure your thigh length from the back of your knee to the back of your hip. The seat should support this full length minus 2–3 finger-widths. Most adjustable chairs offer 40–80mm of seat depth adjustment — sufficient for most adults. If you have very short thighs (under 45cm) or very long thighs (over 55cm), check the seat depth range before ordering.

Seat Width

Your hips should fit comfortably within the seat with a small amount of clearance — approximately 2–5cm each side. Measure across your hips at their widest point. Standard seat widths on quality ergonomic chairs range from 430–540mm — most adults fit comfortably in the middle of this range.

Backrest Height

The backrest should reach at minimum to your mid-back at the level of your shoulder blades. A high-back chair reaching to or above the shoulders provides the most support during extended seated work. Measure from the seat surface to the top of your shoulder blades while seated upright.

Weight Capacity

All chairs have a maximum weight rating. Most quality ergonomic chairs are rated to 110–160kg. If you are above 130kg, always check the weight capacity of the specific chair before purchasing. The Steelcase Leap V2 is rated to 160kg. The Herman Miller Aeron Size C is rated to 159kg. Most standard task chairs are rated to 110–120kg.

Height-Specific Recommendations

Under 5'4" (163cm)

Look for: Herman Miller Aeron Size A, chairs with seat height ranges starting at or below 42cm, adjustable seat depth, and lumbar support that can be positioned low on the backrest. Avoid chairs with fixed, high lumbar positions that won't reach your lower back.

5'4"–6'0" (163–183cm)

You are in the ideal range for most ergonomic chairs. The Herman Miller Aeron Size B, Steelcase Leap V2, Humanscale Freedom, and RH Logic 400 will all accommodate you well with standard adjustment ranges.

Over 6'0" (183cm)

Look for: Herman Miller Aeron Size C, chairs with seat height ranges extending to 52cm or above, and high backrests reaching the upper back and shoulders. The Steelcase Leap V2 and RH Logic 400 both accommodate taller users well. Avoid chairs where the backrest height is fixed and doesn't reach your mid-back when properly seated.

Still Not Sure?

Contact us before ordering. Tell us your height, weight, and any specific requirements — we'll recommend the right chair and size for you. We'd rather spend five minutes on a call than have you receive the wrong chair.

Browse our full range of refurbished ergonomic office chairs, or read our complete ergonomic chair buying guide.