i-Size (ECE Regulation 129)

A new standard for safer child restraints

i-Size restraints can be used in any i-Size seating position and must be installed according to the vehicle manufacturer's instructions

i-Size restraints can be used in any i-Size seating position and must be installed according to the vehicle manufacturer's instructions

ECE Regulation 129 (i-Size) is a new standard for child car seats now running in parallel with the more familiar ECE Regulation 44 (R44).

The new standard came into force in July 2013 but the amendments to UK legislation required to permit use of i-Size child restraints weren't completed until spring 2015*.

Under R44 child seats are approved in one or more overlapping weight groupings** which can be confusing and may encourage parents to switch to carrying children in forward facing seats too early.

No defined groups

In contrast, under the i-Size standard there are no defined groups. Any child restraint can be used up to the maximum child's stature (natural standing height) specified by the child restraint manufacturer. There are some minimum requirements for i-Size regarding stature and direction of travel:

  • Rear facing may be applied to any age of child
  • Restraint for children up to 15 months must be rear facing
  • Restraint for children up to 15 months must accommodate at least a child with a stature of 83cm
  • Forward facing child restraint shall not be designed to accommodate a stature below 71cm
  • A convertible seat in rear-facing configuration must accommodate children up to at least 83cm in height

An i-Size seat can only be attached to the car using Isofix anchorage points.  The child is restrained by an integral harness in the seat and there is no option to install i-Size restraints using adult belts.

Advantages of i-Size

  • Parents are more likely to know their child's height than weight so it should be easier to tell if a seat is suitable and when it's time to move on to a bigger seat.
  • i-Size seats keep children rear-facing for longer - rear facing is safer in a frontal crash.
  • i-Size approval includes a side impact test so seats should offer better all round protection, particularly to the child's head and neck.
  • Use of Isofix should make fitting easier compared to seats fitted using adult belts.


Check the vehicle handbook

i-Size restraints can be used in any 'i-Size approved' seating position and must be installed according to the vehicle manufacturer's instructions.

Check your vehicle handbook first to see if any seating positions are  'i-Size approved'.

Vehicle manufacturers have only been able to get "i-Size approval" since July 2013 when the regulation came into force.

Vehicle specific Isofix

You may be able to use an i-Size child restraint in car seating positions equipped with Isofix anchorage points but not identified in the vehicle handbook as i-Size approved but only if those vehicles/seating positions appear in a vehicle specific application list supplied by the child restraint manufacturer.

Multiple vehicles

If you intend to use the child restraint in more than one vehicle it is important to check that all have i-Size approved seating positions or appear on a vehicle specific application list.

Extreme hazard warning

You must not use a rear-facing child seat on a passenger seat where an active passenger airbag is fitted. The child's head will be too close to the airbag and severe injury or death could result if the bag is triggered.

For forward facing child restraints it is acceptable to leave the airbag active and move the car's seat back on its runners as far as it will go. Do check the car handbook for model specific advice though as airbag size and performance does vary.


(2 April 2015)


*Amendments to:
The Motor Vehicles (Wearing of Seat Belts by Children in Front Seats) (Amendment) Regulations 2015, and
The Motor Vehicles (Wearing of Seatbelt) (Amendment) (No 2) Regulations 2015
completed parliamentary process and came into force on 27 March and 1 April respectively.

**group 0 (0 to 10kg), group 0+ (0-13kg), group 1 (9-18kg), group 2 (15 - 25kg), group 3 (22-36kg)