i-Size Explained: What Does It Mean for Your Car Seat?

i-Size is the name of the European standard R129 for car seats. It replaced the older weight-based classification, and that mainly changes how you choose a car seat.

Length Instead of Weight

Under the old standard, you chose based on weight groups. With i-Size, you choose based on your child’s height. This is more accurate, because the seat height and shoulder height determine whether the seat belt fits properly.

Longer backward

The i-Size standard requires that a child travel in a rear-facing position until at least fifteen months of age. That is the most significant change to the standard, and the reason why many i-Size car seats recline further backward than their predecessors.

Isofix and support leg

i-Size car seats are usually installed using Isofix, often with a support leg or Top Tether. This reduces the risk of incorrect installation, which is the leading cause of unsafe use in practice.

What does that mean when you're shopping?

Look at the height range on the label, not the age on the packaging. Measure your child and compare. If you're unsure between two chairs, choose the one with the longest usable period.

Find out which car seat is appropriate for each age group.