UN R129 (ECE R129) explained: the i-Size child restraint regulation
What UN Regulation No. 129 covers, how it is structured, and where to find each requirement — from the eight seat categories to the 2026/2027 deadlines.
UN Regulation No. 129 — usually called ECE R129 or by its best-known category name, i-Size — sets the uniform conditions for approving Enhanced Child Restraint Systems (ECRS) used in motor vehicles. It is a regulation under the UNECE 1958 Agreement, so an approval granted by one contracting party (shown by the “E” mark) is recognised by the others that apply it.
This site summarises R129 as consolidated up to Supplement 4 to the 04 series of amendments, which entered into force on 4 June 2026 and was published by the EU as Official Journal document 2026/1534.
What R129 changed compared with R44
R129 was introduced in 2013 to sit alongside the older R44. Its core ideas are now familiar to parents and buyers alike:
- Stature-based sizing. A seat is approved for a size range in centimetres, so parents choose by the child’s height §2.8.
- Longer rear-facing travel. Children under 15 months may only use rearward- or lateral-facing seats §6.1.2.7.
- Side-impact testing. Every category except booster cushions and built-in seats is tested in a lateral impact with an intruding door §7.1.3.
- Q-series dummies with more instrumentation (head, neck, chest, abdomen) replace the P-series used under R44 Annex 8.
- ISOFIX-first, “i-Size” compatibility. An i-Size seat fits any i-Size seating position of an i-Size vehicle without a car fitting list §2.3.1.
See the full comparison on R129 vs R44.
How the regulation is organised
| Part | What it covers | Read on this site |
|---|---|---|
| §1–2 | Scope, definitions, the eight categories | Categories |
| §3 | Application dossier for approval | Type approval & CoP |
| §4–5 | Markings, labels and the approval mark | Markings & approval label |
| §6.1–6.3 | Installation, configuration, stature, dimensions, ISOFIX and support legs | Stature, ISOFIX, Boosters |
| §6.6–6.7 | Performance of the assembled seat and its components | Injury criteria, Component tests |
| §7 | Test procedures | Dynamic tests |
| §8–13 | Test reports, production qualification, CoP, extensions | Type approval & CoP |
| §14 | Information for users and packaging notices | Instructions & packaging |
| §16 | Transitional provisions | Series & deadlines |
| Annexes 1–27 | Forms, test equipment, dummies, fixtures, measuring devices | Q-dummies |
Key numbers at a glance
| Requirement | Value | Paragraph |
|---|---|---|
| Rearward- or lateral-facing only, for children under | 15 months | §6.1.2.7 |
| Forward-facing seats may not be designed below | 76 cm | §6.1.2.7 |
| Rear-facing seats for children up to 15 months must fit at least | 83 cm | §6.1.2.7 |
| Infant carrier maximum stature | 87 cm | §6.1.2.8 |
| Booster seats and cushions — lowest stature | 100 cm / 125 cm | §6.1.3.3, §6.1.3.6 |
| Booster seat lateral protection required up to | 135 cm | §6.1.3.3 |
| ISOFIX seat + largest child, maximum mass | 33 kg | §6.3.2.3 |
| Frontal / rear test speed | 50 / 30 km/h | §7.1.3.1 |
| Top tether strap length, minimum | 2 000 mm | §6.3.4.2.2 |
| Buckle opening force (no load) | 40–80 N | §6.7.1.7.2 |
Who needs to know R129
Manufacturers and brands design and approve seats to it. Importers, distributors and retailers need to check that the products they place on the market carry valid approvals for the series accepted in their country. Parents mostly need two things: the stature range on the label, and whether the car has i-Size or ISOFIX positions. Start with the size checker if that’s you.
Tell us the categories and stature ranges you need. Our factory builds child car seats to UN R129 for brands and distributors, and supports you through Technical Service testing and type approval.
This page summarises UN Regulation No. 129 as consolidated up to Supplement 4 to the 04 series (published in the EU Official Journal as 2026/1534). It is guidance, not legal advice: only the authentic UN/ECE texts have legal effect, and approval decisions rest with the Type Approval Authority and its Technical Service.