R129 seats
i-Size and R129 child car seats
GOV.UK identifies legal height based restraints by a capital E in a circle and R129 on the approval label. These seats are commonly called i-Size seats. They must remain rear facing until the child is over 15 months old.
These rules apply in Great Britain.
Rules and figures checked on 10 September 2026.
R129 uses the child's height
The approval label states the height range for the seat and may also state a maximum weight. The child must fit those printed limits, and the seat must be fitted in the vehicle as the manufacturer specifies.
R129 and ECE R44 are different approval systems. GOV.UK still lists approved R129 height based seats and approved ECE R44 weight based seats as legal choices in Great Britain.
Rear facing is mandatory through 15 months
A height based seat must be rear facing until the child is over 15 months old. A forward facing height based seat is permitted only after that age, if the seat label covers the child's height and weight.
Common questions
- What must an R129 approval label show?
- GOV.UK says it must show a capital E in a circle and R129. Check the same label for the height and any weight limit.
- Is R44 still recognised in Great Britain child seat law?
- Yes. Current GOV.UK guidance lists approved ECE R44 weight based seats as well as approved R129 height based seats.
- When can a child use an adult seat belt?
- A child can use an adult seat belt from their 12th birthday or once they reach 135 cm tall, whichever happens first. The belt must be worn where one is fitted.
Related pages
- Child car seat law and seat checkerIn Great Britain, a child normally needs an approved child car seat until their 12th birthday or until they reach 135 cm, whichever happens first. The seat must match the child's height or weight and be fitted as its manufacturer directs.
- Rear facing child car seat lawA height based R129 seat must face the rear until the child is over 15 months old. A rear facing baby seat must never be placed in front of an active frontal airbag.
- Booster seat law by height and weightUnder ECE R44, group 2 covers 15 kg to 25 kg and group 3 covers 22 kg to 36 kg. Approved R129 boosters instead use the height range and any maximum weight printed on their label.
- Backless booster seat lawFrom 9 February 2017, manufacturers could introduce new backless booster models only for children at least 125 cm tall and at least 22 kg. Existing approved group 2 cushions were not withdrawn by that change.
Sources
Each legal threshold and exception above comes from the linked government guidance.