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Last checked: 10 November 2026
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Short answer: R129 is the newer safety standard for child car seats, and i-Size is the name it’s usually sold under. R129 seats are chosen by your child’s height rather than weight, keep children rear-facing until at least 15 months, and are tested for side impacts. Older R44 seats are still legal to use in the UK.
If you’ve started looking at car seats, you’ll have seen “i-Size”, “R129” and “R44” on almost every product page. This guide explains what they mean in plain English, what changed with the newer rules, and what to check before you buy.
In this guide
- What do i-Size and R129 mean?
- How R129 differs from R44
- How to tell if a seat is R129
- Is my R44 seat still legal?
- Choosing by height
- i-Size and your car
- Booster seats and R129
- UK car seat law in brief
- Quick checklist
- Frequently asked questions
What do i-Size and R129 mean?
R129 is the number of a United Nations safety regulation for child car seats (its full name is UN ECE Regulation 129). It was introduced in 2013 to replace the older standard, R44.
i-Size is the name used for the first and best-known part of R129. In everyday shopping, “i-Size” and “R129” are used to mean the same thing: a car seat approved to the newer rules. You’ll often see both on the box.
How R129 differs from R44
The main changes are about how seats are chosen and how they’re tested.
| R44 (older seats) | R129 / i-Size (newer seats) | |
|---|---|---|
| How you choose a seat | By your child’s weight, using “groups” (for example Group 0+ for 0–13kg) | By your child’s height, using the height range shown on the seat |
| Rear-facing | Group 0 and 0+ seats are rear-facing; Group 1 seats can face forwards from 9kg | Must stay rear-facing until your child is over 15 months old |
| Side impact test | Not required | Required |
| Fitting | Seat belt or ISOFIX | Mostly ISOFIX for younger children, designed to reduce fitting mistakes |
| Can you still buy them in Great Britain? | Yes | Yes |
Keeping babies and toddlers rear-facing for longer is one of the biggest changes. Young children have heavy heads and developing necks, and rear-facing seats spread the forces of a frontal crash across the back of the seat. Safety organisations such as RoSPA encourage parents to keep children rear-facing for as long as their seat allows.
How to tell if a seat is R129
Every approved car seat has an orange approval label, usually on the side or back of the seat. Look for:
- A capital “E” in a circle, followed by a number for the country that approved it
- “R129” (or “ECE R129”) for height-based seats, or “ECE R44” for weight-based seats
- The height range the seat is approved for, for example 40–87cm, and usually a maximum child weight
Only seats with one of these approval labels can be used in the UK.
Is my R44 seat still legal?
Yes. In the UK you can still use an R44 seat, as long as it’s the right group for your child’s weight, is in good condition and is fitted correctly. You don’t need to replace a seat that still fits your child just because a newer standard exists.
In Great Britain, R44 seats can also still be sold. In the EU, sales of new R44 seats ended in September 2024, and the same EU product rules apply in Northern Ireland. If you’re buying new, most seats on sale now are R129 anyway.
Choosing by height
With an R129 seat, you match the seat to your child’s height rather than their weight. In practice:
- Measure your child standing against a wall, without shoes. For babies, use the height in their red book or from your health visitor.
- Check the height range on the seat or in its listing, and the maximum weight too.
- Move up a seat when your child reaches the top of the height range, or the maximum weight, or when their head is level with the top of the seat, following the manufacturer’s instructions.
Height-based sizing is designed to be simpler, because many parents know their child’s height more accurately than their weight.
i-Size and your car
Most R129 seats for babies and toddlers fit using ISOFIX: two metal anchor points between the back and base of your car seat. The car seat clicks onto them, with a support leg or top tether to stop it rotating.
- Check your car has ISOFIX points. Most cars made since 2006 do, usually in the outer rear seats.
- Look for “i-Size seating positions” in your car’s handbook. An i-Size car seat should fit any position marked i-Size.
- If your car isn’t i-Size, check the car seat manufacturer’s vehicle fit list before you buy. Many seats work in older cars too.
- Never fit a rear-facing seat in front of an active airbag. If you fit one in the front passenger seat, the airbag must be switched off.
If you’re planning a travel system, also check that your infant car seat clicks onto your pushchair. Our guide How to choose a pushchair covers what to look for.
Booster seats and R129
R129 also covers seats for older children, including high-back booster seats, which use the car’s adult seat belt and are usually approved from around 100cm.
Backless booster cushions are now only approved for older, bigger children. Under the current rules, new booster cushions can only be made for children over 22kg (or, under R129, usually over 125cm). Existing booster cushions bought under the older rules can still be used.
UK car seat law in brief
- Children must normally use a child car seat until they’re 12 years old or 135cm tall, whichever comes first.
- Only seats with an R129 or R44 approval label can be used in the UK.
- R129 seats must be rear-facing until your child is over 15 months.
- Switch off the front airbag before fitting a rear-facing seat in the front.
- Child car seats must not be fitted in side-facing seats.
For the full rules, see GOV.UK: Child car seats: the law.
Quick checklist before you buy
| Check | What to look for |
|---|---|
| Approval label | “E” in a circle and R129 (or R44) |
| Height range | Covers your child’s height now, with room to grow |
| Maximum weight | Your child is under it |
| Rear-facing | Rear-facing until at least 15 months (longer is fine) |
| Your car | ISOFIX points, i-Size seating positions or the seat’s vehicle fit list |
| Fitting | You can fit it correctly every time; ask for a fitting demo in store |
| Travel system | Clicks onto your pushchair, and whether adaptors are included |
| Second-hand | Only from someone you trust, who can confirm it’s never been in a crash |
Frequently asked questions
Is i-Size safer than R44?
R129 seats are tested to newer, stricter rules, including a side impact test, and keep children rear-facing for longer. But any approved seat that fits your child and your car, and is fitted correctly, meets the legal standard. Correct fitting matters just as much as the label.
Do I have to replace my R44 seat?
No. You can keep using it in the UK as long as it suits your child’s weight and is in good condition.
Can my baby face forwards at 15 months?
In an R129 seat, 15 months is the earliest your child can face forwards, not a target. Many seats let children stay rear-facing for much longer.
Is it safe to buy a second-hand car seat?
Only if you know its full history. A seat that’s been in a crash can be damaged in ways you can’t see, and it may be missing its instructions or parts. RoSPA advises against buying second-hand seats from strangers.
Keep reading
- Car seats: our guides and comparisons
- How to choose a pushchair: 10 things to check
- Pram vs pushchair vs travel system: what’s the difference?
