What is i-Size?

If you're choosing a new child car seat, you'll almost certainly have come across i-Size. But what is it, and why is it important?...

What is i-Size?

i-Size is a European-wide child car seat safety regulation aimed at improving safety. It's the first additional safety standard introduced under the EU's R129 regulations, and is designed to reduce the risk of child car seats being installed incorrectly. 

The R129 regulations were introduced in 2013 and are running alongside the old R44 regulations until September 2024, when R44 seats can no longer be sold. R129 introduces improvements in child seat safety in a number of areas. R129 compliant seats must pass a side impact crash test, whereas this isn't required for R44 seats, R129 seats keep children rearward facing until they are at least 15 months old or 76cm tall, while those in R44 seats can face forwards at nine months or when they weigh 9kg; and R129 crash test dummies provide far more information than those used in R44 tests. 

i-size label

Not all R129 seats are also i-Size seats. i-Size seats come with an additional assurance that they will fit into all i-Size certified cars. This means buyers can be reassured that if they buy an i-Size seat for an i-Size car it will fit correctly. To ensure correct fitting, all i-Size seats are no more than 44cm wide.  

Read more: The safest car seats tested

Although R129 seats can be secured either by a seatbelt or Isofix mounts, i-Size seats only have Isofix points; this makes them easier to install and less prone to fitting issues. If you want an i-Size seat, look for the yellow i-Size label on the seat. 

R129 i-Size child seat groups

40cm to 85cm (baby seats)

These seats are usually lightweight infant carriers that are easy to get in and out of a car while the baby is still in the seat, making it easier for parents to transport babies. They generally have quick-release catches to remove the seat from its base with one hand, and a carry handle that also acts as additional crash protection. 

Many infant carriers have extended lie-flat settings that enable the baby to be positioned almost flat in the seat, which is the optimal position for ease of breathing. Another useful feature is a rotating function that enables the carrier to be fitted into the car facing the parent and then swivelled into the correct rearward-facing position. 
40cm to 105cm (toddler seats)

These seats can generally be used for children aged up to four years old. They are larger and heavier than infant carriers and better suited to being left in one vehicle. Although many are suitable from birth, they are quite often used as second stage seats for children aged 15 months and older because the children can walk to the car and climb in and out of the seat. 
Toddler seats must be used rearward facing until a child is 15 months old and then many can be swivelled round so the child faces forwards.  
40cm to 125cm (extended rearward facing seats)

Safety experts recommend that children should be kept rearward facing for as long as possible because this provides the best protection for their heads and necks in collisions, and there are a growing number of extended rearward-facing seats available. While these are among the safest seats you can buy, they can be bulky and require a lot of space in a car. Some seats have reclining features so babies can travel lying down, and footrests are fitted to some seats to help older children find a comfortable position for their legs. 

40-100cm to 150cm (multi-age seats) 

If you want one cost-effective seat that will be suitable from birth right up to the age of 12, check out multi-age seats. They do not have removable seats so aren’t as convenient as infant carriers for babies, and they are often heavy so aren’t that easy to transfer from one car to another. However, they represent great value for money and are ideal for grandparents who may need to only transport children occasionally or need to carry children of different ages.