What is i-Size?

You’ll often see the terms i-Size and R129 used together - and sometimes interchangeably.

But they’re not the same thing.

What is R129?

R129 is the current European car seat safety regulation.

It sets the rules for how car seats are:

• Tested

• Approved

• Used

R129 introduced:

• Height and weight-based sizing (cm and kg) instead of weight groups

• Mandatory side impact testing

• Improved crash test standards

So if a seat is approved to R129, it meets these newer safety requirements.

What is i-Size?

i-Size is a category within R129.

Think of it like a “sub-group” with additional criteria.

To be labelled i-Size, a seat must:

• Be installed using ISOFIX

• Meet specific size compatibility standards

• Fit within defined vehicle seating dimensions

So what’s the difference?

• All i-Size seats are R129

• Not all R129 seats are i-Size

That’s the key takeaway. Like fingers and thumbs!

Why does this matter?

You might see:

• A seat labelled R129 (but not i-Size)

• A seat labelled i-Size

Both are approved under the same regulation, but:

• i-Size seats follow stricter fit and compatibility rules

• Non-i-Size R129 seats may offer more flexibility (e.g. seatbelt installation)

Does i-Size mean safer?

Not necessarily.

Both i-Size and non-i-Size R129 seats:

• Meet the same core safety regulation

• Pass the same crash testing standards

The most important thing is still:

• A good fit for your child

• Compatibility with your vehicle

• Correct installation and use

Quick summary

• R129 = the regulation

• i-Size = a category within R129

• All i-Size seats are R129

• Not all R129 seats are i-Size