ISOFIX, i-Size, ECE R129 and ECE R44/04 – not the easiest terms to understand when it comes to your child’s safety. If you’re unsure as to what the lingo means, you’re not alone.

A 2017 study by Which found that 53% of parents of babies hadn’t heard of i-Size, whilst a further 25% were aware of it but didn’t know what it was.

Many parents are unfamiliar with the often complicated world of children’s car seat regulations. That’s why we’ve busted the jargon and broken it down for you in our easy-to-follow guide.

Precious Little One i-Size Car Seat Jane Gravity i-Size Car Seat (Jet Black)

Jane Gravity i-Size Car Seat (Jet Black)
Allows rear-facing travel for up to 4 years


What Is i-Size?

To ensure all car seats are fit for purpose, they are manufactured and tested according to strict criteria. The new European regulations which set out these requirements are called ‘i-Size.’ Introduced in July 2013, i-Size forms part of a wider safety standard, ‘ECE R129’, which itself came into force in the UK in April 2015.

What i-Size aims to do is maximise child safety. It ensures that all car seats are fitted to cars using an anchoring system called ‘ISOFIX’, which attaches car seats directly to the frame of your car. Unlike their predecessors, i-Size car seats have been tested with specially-created ‘Q-Series’ (infant to child) crash test dummies.

Why Is i-Size Necessary?

  1. Reduces the risk of installation errors
  2. Protects infants from head and neck injuries
  3. Safeguards against side-impact collisions
  4. Prevents early up-sizing by using height instead of weight
  5. Encourages the use of safer ISOFIX child seats

Precious Little One i-Size Car Seat Britax Romer DUALFIX i-SIZE Car Seat (Sand Marble)

Britax Romer DUALFIX i-SIZE Car Seat (Sand Marble)
Installation indicators confirm correct installation


Is My Car Seat Safe?

So long as it meets ECE R44/04 regulations, yes. These have a label showing a capital ‘E’ in a circle and ‘ECE R44.’ Child car seats approved outside of the EU cannot be used in the UK.

If you choose to not buy an i-Size seat, experts recommend keeping your baby rear-facing for as long as possible. Move them to a forward-facing seat only once they can sit up unaided and have exceeded the maximum weight or height for the baby seat. Consider using a rear-facing Group 1 seat for longer.

Does i-Size Replace ECE R44/04?

i-Size does not replace the current regulation, it merely runs alongside it. Why is this the case?

  • Seat belts were enforced as part of UK car manufacturing in 1980, yet only when they became common on the roads did it become law to actually wear them.
  • Similarly, you can still use and buy non i-Size car seats until at least 2018, as long as they meet the ECE R44/04 regulations. Though with added safety benefits, you might choose to upgrade to i-Size.
  • When i-Size replaces ECE R44/04 in its entirety, you won’t be able to buy new ‘old-style’ seats, though you will still be allowed to use them for some time (possibly a few years) thereafter.


ECE R44/04 vs. ECE R129 (i-Size)

There are a number of key differences between the old regulation (ECE R44/04) and i-Size child car seats:



How Do I Know If My Car Seat Is i-Size?

Precious Little One i-Size Car Seat (5)

Your car seat is i-Size compatible if it has the logo displayed above. It is similar to the ISOFIX logo but has an ‘i’ on the side. Many suitable car seat models have the letter ‘i’ in their name or include the word ‘i-Size.’

Precious Little One i-Size Car Seat Maxi-Cosi AxissFix Air i-Size Car Seat (Nomad Grey)

Maxi-Cosi AxissFix Air i-Size Car Seat (Nomad Grey)
World’s First Car Seat With Airbags


Do i-Size Car Seats Fit All Cars?

No, even cars that have ISOFIX fittings will not fit all i-Size car seats safely. You will need to check that your car model is on the fitting list for the specific i-Size car seat that you want.

Cars manufactured after 2011 have ISOFIX fittings as standard. If you have an older car, you might be able to use an ISOFIX conversion kit to make it compatible with your i-Size car seat. Kits cost around £17 and take about an hour to fit, for about £90.

However, the older your car is, the less likely it is to be compatible with the kit. Cars made before 1997 will not be able to accommodate any i-Size car seat.

Check the compatibility of your car using the car seat compatibility tool from The Royal Society for the Prevention of Accidents and the Department for Transport.

What Ages Do The Regulations Cover?

Under UK law, children must use a child car seat until they are 12 years old or 135cm/4ft 5in tall, whichever comes first. However safety experts recommend that all children under 150cm/4ft 11in use a child car seat, as is the legal requirement in other European countries. For children weighing more than 36kg (5st 10lb) but under 150cm/4ft 11in, it is advised to go by height.

At present i-Size car seats only cater for children up to 105cm tall (about 4 years old). However, it is likely that i-Size car seats for older children will form a later part of the regulations. If these legal requirements are ignored the consequences can be expensive (at best) or fatal (at worst). On the spot fines of up to £30 are applicable, or up to £500 if referred to court.

Precious Little One i-Size Car Seat Britax Romer TRIFIX 2 i-SIZE Car Seat (Mystic Black)

Britax Romer TRIFIX 2 i-SIZE Car Seat (Mystic Black)
Suitable for forward facing travel from 15 months


Types Of i-Size Car Seats

We’ve hand-picked a number of i-Size car seats, featured throughout this article, perfect for your precious little one before they reach 15 months and thereafter.

For even more options, view the full i-Size car seat collection from Precious Little One, complete with essential car seat bases for safe travel.


Did you enjoy this article?

face-1 face-2 face-3 face-4


About the author: Charlie Hardy

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.