Office chair glossary: parts, mechanisms and standards

The parts named in this glossary, on a schematic task chair.

1D, 2D, 3D, 4D armrests: Shorthand for how many ways an armrest adjusts: 1D usually means height only; 4D adds width, depth (forward and back) and pivot. EN 1335-1 Types A and Ax require armrests adjustable at least in height and width. See EN 1335 explained.
ANSI/BIFMA X5.1: The North American safety and durability test standard for general-purpose office chairs. The 2017 edition tests with a 275 lb (about 125 kg) user. It has no dimensional requirements. See EN 1335 vs BIFMA.
ANSI/BIFMA X5.11: The North American standard for large-occupant office chairs, for users up to 400 lb (about 181 kg), with a minimum seat width. See chairs for heavier people.
BIFMA LEVEL: A multi-attribute sustainability certification based on the ANSI/BIFMA e3 standard, with three levels and a third-party audit. Not the same as BIFMA X5.1. See sustainable office chairs.
Blauer Engel (Blue Angel): The German federal ecolabel. Upholstered office swivel chairs are certified under DE-UZ 117, the criteria for low-emission upholstered furniture; there are no criteria written only for office chairs. See sustainable office chairs.
Castor: The wheel under each leg of the base. Hard floors and carpet need different castors; EN 1335-1 requires castor and floor guidance in the user information. See repair and spare parts.
Cradle to Cradle Certified: A product certification in five categories with Bronze, Silver, Gold and Platinum levels; the overall level is the lowest category level. "Cradle to cradle principle" without "Certified" is a design claim, not a certification. See sustainable office chairs.
DSE Directive (90/270/EEC): The EU directive on work with display screen equipment. Its Annex requires a stable work chair with adjustable seat height, a seat back adjustable in height and tilt, and a footrest for anyone who wants one. See the DSE Directive.
EN 1022: The European standard for the stability of seating. EN 1335-2:2018 still cites its 2018 edition. See EN 16139 and EN 1728.
EN 1335: The European standard for office work chairs. Part 1 sets dimensions by Type; part 2 sets safety, strength and durability for users up to 110 kg, 8 hours a day. Part 3 has been absorbed into part 2. See EN 1335 explained.
EN 16139: The European standard for the safety, strength and durability of non-domestic seating other than office work chairs, such as visitor chairs, with Level 1 (general) and Level 2 (extreme) use. See EN 16139 and EN 1728.
EN 1728: The European test methods for the strength and durability of seating. It sets no limits; the requirement standards (EN 1335-2, EN 16139) do. See EN 16139 and EN 1728.
EPD (Environmental Product Declaration): A third-party verified life-cycle assessment report under ISO 14025, in Europe usually to EN 15804. It reports figures such as a carbon footprint; it is not a pass-or-fail label. See sustainable office chairs.
EU Ecolabel: The EU’s official ecolabel. Its furniture criteria (Decision (EU) 2016/1332, valid to 2029) include office chairs and exclude refurbished furniture. See sustainable office chairs.
Footrest: A support for the feet when the seat must sit higher than the legs need, usually to match a fixed desk. Under the DSE Directive, employers must provide one on request. See chairs for shorter people.
Forward tilt: An adjustment that lets the seat pan tilt forward a few degrees, opening the hip angle for desk work. EN 1335-1 requires at least 5° of seat-angle adjustment where the seat angle adjusts. See the chair register.
Gas lift (gas spring): The cylinder in the column that sets seat height. A chair that keeps sinking usually has a worn gas spring; EN 1335-1 requires a warning that only trained personnel may replace it. See repair and spare parts.
GS mark: Geprüfte Sicherheit, a German statutory safety mark under ProdSG § 20: a type test, factory inspection and ongoing checks by an accredited body, valid for at most five years. See office chair standards.
ISO 24496: The international method for measuring office chair dimensions, using a 64 kg loaded template. EN 1335-1:2020 measures this way. See EN 1335 explained.
Kneeling chair: A seat tilted forward with shin rests and, usually, no backrest, such as Varier’s Variable. Not a task chair under EN 1335. See kneeling and saddle chairs.
Legal guarantee: The seller’s liability, under Directive 2019/771, for defects that become apparent within at least two years of delivery. Separate from, and not reduced by, any manufacturer warranty. See warranty and guarantee.
Lumbar support: Support for the small of the back. EN 1335-1 places it 170–300 mm above the seat, adjustable in height on Types A and Ax. See chairs and back pain.
Möbelfakta: A Swedish ISO 14024 Type I label for furniture covering quality, environment and supply chain, owned by IVL and the furniture federation TMF. See Scandinavian chairs.
Nordic Swan Ecolabel: The Nordic countries’ official ecolabel. Its furniture criteria (031) cover wood sourcing, chemicals, a quality test and warranty and spare-parts requirements. See Scandinavian chairs.
Popliteal height: The height from the floor to the underside of the thigh just behind the knee, sitting with the thigh level. Seat height should roughly equal popliteal height plus shoes. See the height calculator.
Quality Office: A German certification run by the industry body IBA. It requires the GS mark and adds ergonomics, durability and sustainability criteria. See office chair standards.
Recline lock: A control that holds the backrest at one or several positions. Chairs without it recline freely against the tension setting. See the chair register.
Saddle chair: A high, saddle-shaped seat on a gas lift that opens the hip angle with the feet on the floor, such as the HÅG Capisco. See kneeling and saddle chairs.
Seat depth: The distance from the backrest to the front edge of the seat. It should let you sit back with a small gap behind the knee; Type A seats must adjust over at least 70 mm. See EN 1335 explained.
Seat height: The height of the top of the loaded seat above the floor. EN 1335-1:2020 Type A chairs must cover 400–520 mm. See the height calculator.
Spec Index: Our 0–100 score computed only from published specifications: adjustability, seat-height span, load rating and standards, warranty and environmental documents. It is not a comfort rating. See how we score.
Synchro mechanism: A tilt mechanism in which the seat and backrest recline together, the backrest moving further than the seat, so you stay supported as you lean back.
Tension (recline tension): How hard the backrest pushes back as you recline. It is set by a knob (manual) or adjusts itself to your weight (automatic, weight-sensitive mechanisms). See the chair register.
Type A, Ax, B, C: The four chair Types of EN 1335-1:2020. Ax and A adjust most and cover the widest range of people; B and C allow some fixed dimensions. Seat-height ranges: Ax 400–540, A 400–520, B 420–510, C 430–480 mm. See EN 1335 explained.
Withdrawal right: The consumer’s right, under Directive 2011/83/EU, to cancel an online purchase within 14 days of receiving the goods without giving a reason. Goods made to the consumer’s specifications are excluded. See buying across borders.

Cite this page

Best Office Chairs Europe, “Office chair glossary”, https://bestofficechairs.eu/glossary/, updated 20 October 2026.