Child car seats: Choosing a child car seat Car seat weight groups

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How do you know which type of child car seat to choose?

The weight, not the age, of your child is the more important factor when changing groups

Child car seats are split into groups according to the weight of the child they're designed to protect. 

These groups are defined by United Nations safety regulations and cover children from birth all the way up to 36kg (about 11.5 years for boys and 11 years for girls). 

Each child car seat is tested by the manufacturer to ensure that it provides a minimum level of protection for children of the weight range covered by its group. 

So, when choosing a child car seat, the first thing to remember is that your child’s weight is a more important factor than his or her age. 

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.

Child car seats: weight groups

There are five main weight groups for child car seats - use this table to work out which one you'll need to go for.

It's also possible to buy seats that combine one or more groups, such as 0+ 1 (0-18kgs), 1-2-3 (9-36kg)  or 2-3 (15-36kg). 

These can appear to be a more economical way of buying a child car seat as they will last your child for longer. Find out if we recommend combined Group 1-2-3 child car seats.

What are the car seats in each group like?

The seats in each group are designed to protect the most vulnerable parts of a child from crash injuries as it grows from baby to teenager.

Group 0 and 0+ - infant carriers and baby car seats 

A rear-facing Group 0+ child car seat installed with an adult seat belt or on an Isofix base

Group 0 seats (for babies up to 10kg) are rare these days. They have been superceded by rear-facing Group 0+ seats, which will last a bit longer because they are suitable for children up to 13kg (roughly 12-15 months). 

Key features:

• Rear facing to support and protect an infant's head, neck and spine.
• Protective shell, head support and padding.
• Secured to the car via a base (Isofix or belted) or the adult three-point seat belt.
• Five-point harness to restrain the baby; some have a one-pull harness tightener.
• Semi-supine position (45-degree recline angle to provide good support for a baby's head and neck).
• Handle to make it easier to put the seat in your car with the baby inside. 
• Shaped bottom so it can be used as a rocking seat.
• Some models can fit on a pushchair chassis (with or without adaptors) to be used as part of a travel system.

Choose the best seat for your child with our reviews of Group 0+ child car seats.

Although some infant carriers are designed to be used on a pushchair and in the home, babies - particularly premature or newborn ones - should not be left in their car seats for long periods. This can affect their breathing in as little as 45 minutes.

A Group 1 child car seat with harness

Find out all you need to know about buying the best for your baby with our free downloadable guide to buying for your baby, created in conjunction with the NCT.

Group 1 - toddler seats

Group 1 seats are usually forward facing, although extended rear-facing Group 1 seats are becoming more common in the UK.

Key features:

• Protective shell and padding.
• Secured to the car via a base or the seat belt.
• Five-point harness or impact shield to restrain the toddler.
• Adjustable head support.
• Removable seat liners and adjustable harness position to provide more space for growing babies.
• It's possible to recline some seats to give a more comfortable sleeping position.

Find the right seat for your toddler - use our tool to compare Group 1 child car seats.

Group 2 and 3 - booster seats

Group 2 and 3 seats are designed to raise children up from the car's existing seat so that the adult three-point seat belt is positioned correctly across the pelvis, chest and collarbone.

This Group 2-3 child car seat has adjustable headrest and side-protection for growing kids

Key features:

• You use the three-point adult belt to restrain the child.
• You use belt guides to position the adult seat belt on the child.
• Adjustable headrests move upwards as the child grows.
• Some seats have attachments to the car's Isofix mounts to keep the seat secured in the car when it's not belted in.
• Some seats also offer adjustable side-impact protection, reclined positions and drink holders.

Read our reviews of Group 2 and Group 3 child car seats.

Some booster seats have backs that can be removed as children grow bigger. You can also buy booster cushions that do not have a back.

We strongly recommend that you don't remove the back of high-backed booster seats or use a backless booster cushion.

This completely removes any side and head protection from the child car seat, leaving kids vulnerable to head and side injuries, particularly in side impacts (which make up a quarter of all car accidents). 

It also makes it more difficult to position the diagonal strap of a three-point adult seat belt correctly across the shoulder.

Child car seat crash test video

Our tests prove that backless boosters leave your child vulnerable to head, neck and impact injuries. Watch our video to see this in action.

Moving up through the child car seat groups

Generally we advise that you try to keep your child in the lower-group child car seat for as long as you can -  but make sure you don't leave it until your child is over the car seat's weight limit before changing.

Changing to forward facing

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

Moving up a group

In most cases, the child will reach the weight limit of a child car seat before becoming too tall for it.

Children at the bottom weight of each weight group are more vulnerable to injuries. The recommended weights for each group overlaps, so we advise you to let your child reach the top weight for one group rather than swapping when they reach the bottom weight of the next.

Your 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.

More on this...

• See which child car seats are safest in our child car seat reviews
• Find out how we test child car seats
• Make sure you buy the safest and most efficient car with our car reviews