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Which car seat?

Car seat groups

By Lisa Galliers

Article 2 of 6

Your child's weight is an important factor in choosing a car seat; here we break down the car seat weight groups to show you which you need.

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Child car seats are bought in two ways, either according to your child's car seat weight group or according to the height of your child. 

Each child car seat is tested by the manufacturer to ensure that it provides a minimum level of protection for children of the height or weight range covered by the seat. So, when choosing a child car seat, remember to go by your child’s height and weight.

Here we're going to explain about the different car seat weight groups. The weight groups are defined by United Nations safety regulations and, in the UK, cover children from birth all the way up until they are 12 years old, 135cm in height, or about 36kg. In the picture above you can see (from left) a group 0+ child car seat, group 1 and a group 2/3 seat. You can find out below what these group numbers mean for your baby or child.

Moving babies and younger children up to the next group before they reach the maximum weight for their seat could lead to more severe injuries in a crash.

Car seat groups
Seat group Weight range Approximate age range Compare car seat reviews
Group 0 0-10kg (0-22lb) From birth to about 6 to 9 months Group 0 car seat reviews
Group 0+ 0-13kg (0-29lb) From birth to about 12-15 months Group 0+ car seat reviews
Group 0+/1 0-18kg (0-40lb) From birth to 4 and a half years Group 0+/1 car seat reviews
Group 1 9-18kg (20-40lb) About 9 months to 4 and a half years Group 1 car seat reviews
Group 2/3 15-36kg (33lb-5st 9lb) About 3 years to 12 years Group 2/3 car seat reviews
Group 3 (booster seats) 22-36kg (48lb-5st 9lb)/125cm About 6 years to 12 years Avoid confusion, read more about booster seat rules
Group 1/2/3 9-36kg (20lb-5st 9lb) From around 9 months up to 12 years Group 1/2/3 car seat reviews
i-Size By height from approx 40cm-105cm. Find out more about i-Size car seats From birth up to 4 years old i-Size car seat reviews

Baby car seats (Group 0+)

Baby car seats (group 0+) are generally smaller and lighter than the car seats you'll buy as your child gets older. They are also rearward facing – that means your baby will be travelling with his or her back to you if you're driving. Research shows it's safest for babies to travel rearward-facing for as long as possible.

Group 0+ car seats will last your baby from birth until he or she is around 12 to 15 months old.

We recommend that you leave your baby in a rear-facing child car seat until they are least 15 months old. See more on rearward facing child car seats further down the page.

Some group 0+ baby car seats are designed so that you can also attach them to a pushchair chassis to form a travel system - the thinking behind this is that you can take your baby from car to pushchair without having to disturb them. For this reason they'll also have a carry handle. However, our advice is to avoid keeping babies, particularly very young ones, in car seats any longer than absolutely necessary.

Group 0+ car seats will last your baby from birth until he or she is around 12 to 15 months old.

Group  0+/1 car seats

Group 0+/1 car seats will last your baby from birth to around four years old. Your baby will initially travel in the seat rearward facing and you can then usually change it to a forward-facing seat. Some seats allow this from 9kg (approximately nine months). We do not recommend you turn your baby forward-facing too soon.

It's best to keep children travelling rearward facing in car seats for as long as possible - at least until they are 15 months old. Many Group 0+/1 models offer the option for your child to travel rearward facing until he or she is up to four years old.

Unlike a baby car seat (Group 0+) a Group 0+/1 car seat will stay in your vehicle. You won't be able to take it out and pop it onto a travel system chassis. Because they are larger than a Group 0+ car seat this type of seat may take up more space in your car.

Group 0+/1//2 car seats

These are designed to last a child from birth to 25kg (approximately six years old). In our experience, children change too much from birth to 25kg  for one seat shell to adequately provide the protection they need at each stage. We've tested some very poor Group 0/1/2 child car seats in the past, which fail to position the adult seat belt correctly on the child and could injure their neck and internal organs in a crash.

Group 1 car seats

Group 1 car seats are for toddlers weighing between 9kg and 18kg. That's from about nine months old up to around four-and-a-half years old. Most car seats on sale that are Group 1 are forward facing, although you can find some that let your child travel rearward facing until he or she is up to four years old. See more on rearward facing child car seats further down the page.

Group 2 car seats

You can't buy a child car seat that is only Group 2. If your child is ready to move up from a Group1 seat the next seat up is a Group 2/3 high backed booster seat.  

Group 2/3 car seats

Group 2/3 car seats are high backed booster seats. They don't have a harness. Instead you'll secure your child and the seat with the car's seatbelt. Some models can still be installed using Isofix to keep them securely attached to the car. A group 2/3 car seat will last your child from 15-36kg. That's from about 3 years to 12 years.

Group 1/2/3 car seats

A car seat that covers more than one car seat group is also known as a multigroup seat. These can appear to be a more economical way of buying a child car seat, as they will last your child for longer, but sometimes our tests find that a seat which covers more than one group doesn't protect as well as it should throughout all three groups. 

There are many Group 1/2/3 seats available, which can be used from nine months all the way up to 12 years (9-36kg). These allow you to secure your baby in a five-point safety harness, then it converts to a high-backed booster seat when your child is older and bigger. Generally, car seats designed to span more than two groups do not always provide good levels of protection in all weight groups, but there are some exceptions.

Backless booster seats - Group 3 car seats

Some Group 2/3 car seats convert to a group 3 seat, which is just a booster cushion. You can also buy booster cushions. These raise the child's body to a height suitable for use with the adult seatbelt, but booster cushions are not as safe as a high-backed booster seat with a full-length back and 'wings', which provide extra protection for the head and chest in a side-impact crash.

A booster cushion satisfies the legal requirement for children up to 1.35m (approximately 4ft 6in) and they're cheap (about £6-£30), but we don't recommend them, especially for younger children. High-backed child car seats are safer, so it's worth paying a bit more for extra protection.

Booster seats, particularly of the backless variety, have been in the news a lot in the last 12 months because of a change in the law that has got people pretty confused.  

To clarify the rules for booster seats:

  • From March 1 2017 the approval rules for booster seats have changed. 
  • These new rules mean that any newly-approved backless booster seat on sale will be limited for use only with children taller than 125cm and weighing more than 22kg.  
  • You will still see other backless booster seats that don't need new approval on sale and approved for use for children of between 15kg and 36kg. 
  • Both seats are legal to use as long as you are following what it says on the label. So always make sure you check the label. 
  • If you already own a backless booster seat you can still use it.

Which car seat groups have Isofix?

Isofix is a child car seat fitting system that comes as standard in all new cars and is built in to lots of older models as well. It's designed to make installing your car seat quick and easy. 

Isofix is a child car seat attachment system which uses metal bar connectors built into the chassis of the car to connect to the child car seat and hold it in place. The connectors are often hidden within the car's seat padding. Once the connectors are clicked together with these anchorage points, the child car seat is secured by a third point, either a support leg which comes built-in to the seat or seat base, or a top tether (a strap that attaches to a mount somewhere behind the rear seat). Both of these work to stop the car seat tipping forward in an accident.

You can find Isofix child car seats in all car seat groups from Group 0+ up to Group 2/3 car seats. You'll often see Isofix in Group 2/3 car seats referred to as Isofit. That's because there is a difference. In Group 2/3 car seats, even though the car seat is attached to the car using the same connectors, your child is kept in the car by the car's seat belt. Whereas in the younger car seat groups, the Isofix car seat is attached to the car using Isofix connectors but your child is kept in the seat by a harness that's attached to the car seat.  

We think it's worth paying extra for Isofit if you're buying a Group 2/3 seat as it means, in the event of a crash, even if there isn't a child in the car seat, it will stay attached to the car, rather than flying forwards at great force and causing injury to other occupants of the car.  If your car doesn't have Isofix connection points, don't worry, just make sure the car seat is belted in before you set off.

Read more about what our car seats testing has discovered about the differences in crash tests results between Isofix car seats and non Isofix car seats.

When to change your child's car seat

Our car seat experts believe that it's better and safer to keep your child in the lowest group seat for as long as possible, rather than moving up groups too early. It's also more economical, too, as you won't have to splash out on a new seat until you've had the maximum usage out of your current seat. Do keep an eye on your baby or child's weight and height though, to make sure they aren't out-growing the seat too quickly.

Changing to forward-facing

The most important change you'll make for your child is switching from a rearward-facing to a forward-facing car seat. Forward-facing Group 1 child car seats are approved to be used from 9kg, but most car seat experts agree this is too soon. 

When you turn your baby forwards you expose them to the danger of their spinal cord snapping in a frontal impact crash - the forward momentum of their big head can overstretch their weak neck muscles and ligaments.

We recommend that you leave your baby in a rear-facing child car seat until they are least 15 months old, or the first of these events occurs:

  • They reach the weight limit of that seat (13kg for Group 0+, 18kg for Group 1)
  • The crown of their head is level with the top of the car seat

Browse Best Buy car seats for every group. 

Moving up a car seat group

As you can see in the image of the little boy above. It's time to swap his car seat. A child will have outgrown a Group 1, 2 or 3 child car seat if his or her eyes are level with the top of the seat when sitting in it. 

In most cases, a child will reach the weight limit of a child car seat before becoming too tall for it, but all babies and children are different.

Children at the bottom weight of each group are more vulnerable to injuries, this is why we don't advise you swap too soon. The recommended weights and heights for each group overlap, so we advise you to let your child reach the top limit for one group rather than swapping when they reach the bottom weight of the next.

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