What are i-Size (R129) child car seats?

Keeping your children safe during car journeys is paramount, and that's why child seats are subject to regulations.

The i-Size regulation, officially known as ECE R129, is the latest European standard for child car seats, and aims to both boost protection for children and simplify the selection process for parents.

i-Size seats are designed for installation using your car's ISOFIX anchor points, reducing the risk of incorrect fitting and improving overall stability. However, it's important to note that while i-Size seats are compatible with ISOFIX, not all ISOFIX seats meet i-Size standards.

What are i-Size child car seats?

i-Size child seats make it easier to find a seat that safely fits both your child and your car. The term 'i-Size' refers to the European car seat safety regulation ECE R129, introduced to improve child protection and simplify seat selection. Unlike the older ECE R44/04 regulation, which categorised seats based on a child’s weight and was phased out by September 2024, i-Size uses height as the determining factor to ensure a better fit.

The aim of i-Size is to standardise car seat compatibility with all vehicles using ISOFIX anchor points, which are now a requirement in all modern family cars. However, not all i-Size seats fit every ISOFIX-equipped vehicle, so checking the manufacturer's compatibility list remains necessary.

How do I know if a car seat is i-Size?

i-Size seats are identifiable by the ‘i-Size’ logo on the seat itself or the packaging. Additionally, many manufacturers include 'i-Size' in the product name. However, for certainty, it's best to check the product details or confirm with a retailer that the seat meets ECE R129 standards. 

How are i-Size child seats grouped?

i-Size car seats are categorised based on a child’s height rather than weight. The main categories are:

• i-Size Infant (45–75 cm): Suitable for newborns up to approximately 12 months old
• i-Size Toddler (61–105 cm): Designed for children from around 6 months to 4 years
• i-Size Child (100–135 cm): Suitable for children aged approximately 4 to 12 years

These height-based categories are intended to ensure a safer, more tailored fit as a child grows.

Why are i-Size seats safer?

i-Size seats offer several key safety benefits compared to older R44/04 models.

The regulations require children to remain in a rear-facing seat until they are at least 15 months old, which significantly reduces the risk of head and neck injuries in an accident. And unlike R44/04 seats, i-Size models undergo side-impact crash tests to ensure additional protection.

When it comes to i-Size seat testing, specialised Q-Series dummies are used. These more accurately simulate real children of different ages and sizes, and provide better safety data.

Because i-Size seats must be installed using ISOFIX anchor points, the chances of incorrect fitting are reduced.

When should I stop using a rear-facing child seat?

Under the United Nations’ R129 regulation, children must travel in a rear-facing seat until they are at least 15 months old. Rear-facing positions provide better support for a child’s head and neck, reducing injury risks in the event of a crash. Although the legal requirement is 15 months, many experts recommend keeping children rear-facing for as long as possible, ideally up to four years old.

Are i-Size seats a legal requirement?

Currently, both ECE R44/04 and i-Size (R129) seats are legal in the UK. However, due to the enhanced safety features of i-Size, R44/04 seats have phased out from sale, meaning i-Size is the only standard for new seats.

Children must use a car seat until they are either 12 years old or 135 cm tall, whichever comes first. However, safety organisations recommend using a booster seat until a child reaches 150 cm.