Child car seats: How to fit a child car seat Factors that affect child car seat fitting

Mum fitting a child car seat

Mum still needs to use the diagonal belt before this child car seat is fitted properly

Buying one of our Best Buy child car seats is a great start towards protecting your family in a crash. 

But not even the highest scoring child car seat can prevent injuries if it's not installed properly in your car.

Labels on child car seats that say 'universal' or 'semi-universal' might give the impression that some car seats will fit any car. 

But a key message to remember when buying a car seat is the opposite - not all car seats fit in all cars. 

How can I find a child car seat that fits?

The best way to do this is to get a qualified and competent car-seat fitter to try a range of seats in your car. 

Ask for an appointment with a trained fitter at the retailer you plan to use, or visit a local council car seat fitting clinic for more help.

To get more practical tips about the buying process, visit our how to buy a child car seat guide.

How your family affects which child car seat will fit

The people that you need to transport will affect the seats you can use in your car.

Number of children

Needing to secure two or more children in a car can affect the amount of space that each seat can occupy.

Although it's generally safest to transport kids in the back seats, you might need to use the front seat to fit the whole family and their car seats into smaller cars.

Height of front seat passengers

Tall passengers might not leave enough space behind them for the car seat or support leg to fit properly.

How your car affects what child car seats will fit

It might sound crazy to say that child car seats might not fit in a car, but the shape of the seats, space in the cabin and features of the car can prevent a seat from fitting properly. 


Airbags inflate rapidly (and then immediately deflate), cushioning people and protecting them from hitting the vehicle interior. 

Airbag warning for child car seats

Take note of the airbag warning label on child car seats

People can be injured if they're too close to an airbag when it inflates. 

To prevent this you should:

  • never put a rearward-facing baby seat in front of an active passenger airbag
  • make sure the passenger car seat is as far back as possible if you use a forward-facing car seat on it
  • make sure that the child restraint doesn't rest against the door where side airbags are fitted or against the airbag panel. 
Cabin space for rear-facing car seats

You need space in front of a rear-facing child car seat

Cabin space

There should usually be an arm's width of space between the top of a rearward-facing infant carrier and the front seat back.

You also need space between the seat back and any support leg for Isofix car seats and bases.

Lap belts

Most belt-fitted child car seats are designed to fit with a three-point diagonal seatbelt. 

Using a lap-only belt could cause the seat to flip over in a crash.


Headrests can cause problems with child car seats

The car's headrest should not interfere with the child car seat

The headrest should not touch your child's car seat, especially if it's forcing the car seat forwards away from the backrest. 

If your headrests can't be removed, you may not be able to use a child car seat in that seat. 

Don't think that using your headrest to jam the seat in place will make your child extra safe. The seat needs to move forwards with the child in a crash to provide good head and neck protection, and jamming it back will stop this from happening.

Seatbelt anchor points

Sometimes the position or design of the seatbelt anchor points makes it difficult to fit a child seat securely. 

If the anchor point is too far forward, the seatbelt webbing can't pull the child seat back and down into the cushion as it should do. 

buckle crunch on a child car seat

Buckle crunch - the buckle, not the seatbelt webbing, is bent around the car seat frame

Length of seatbelt stem

Many new cars have buckles quite close to the seat, but older cars often have the buckle on a longer stem. 

'Buckle crunch' happens when the length of the stem means that the seatbelt buckle bends around the shell of the car seat when it's done up.

This results in a weak connection and puts pressure on the buckle - it could break or come undone in an accident.

You must make sure the fabric part of the seatbelt - the webbing - is holding the seat and not the buckle. In the event of a crash, the seatbelt fabric will stretch to help absorb the impact.

Seatbelt length

Some seatbelts are not long enough to go around a rearward-facing infant carrier (Group 0+ car seat). 

You can sometimes avoid this problem by:

  • using Isofix connectors (if your car and seat have them) to attach the seat
  • choosing a car seat with a base that doesn't require such a long seatbelt to fix it in place
  • using an alternative belt routing designed by the manufacturer to address this problem
  • lowering the seatbelt height adjuster on the door pillar.
Sloping seats affect car seat fitting

The slope of this car seats leaves the child car seat sitting too upright for a baby

Sloping seats

Car seats are shaped to pull passengers into them, so many rear seat benches slope down from front to back and towards the middle. 

This might mean that a child car seat does not sit properly on the seat.

Another problem is that the child inside might be too upright when placed rearward facing, so their head flops forward easily, which could lead to breathing difficulties.

Some manufacturers make wedges to go with their seat if you experience this problem in your car. 

An infant carrier should sit at about 45 degrees to the ground when secured. 

Sloping backrests

Child car seats need good contact with the backrest to prevent them moving around too much in a crash. Check the seat's instruction manual to see what level of contact the seat needs.

Further points for fitting Isofix seats 

under floor storage car compartments

You can't put a child car seat support leg on an underfloor storage compartment lid

Isofix child car seats are usually used with a support leg or top tether to prevent the seat pivoting around the Isofix mounts in a crash. 

This is because pivoting can pitch the child forwards and place strain on their back and neck.

Underfloor storage compartments

Normally, you can't use a base or car seat with a support leg on a seat that has an underfloor storage box in front of it. 

The lid of the storage compartment is not strong enough to stand the forces that the support leg will put on it in a crash. 

If the lid buckles, the support leg won't be able to prevent the seat from pivoting. 

Top tether points for fitting child car seats in a car

Top tether points for fitting child car seats in the back of a car

Top tether points

Some cars or car seats offer tether strap options as an alternative to a support leg.

Top tether straps should only be fixed to a tether point that's been designed to stand up to the force of a child car seat pulling away from it in a crash. 

Headrests are not designed to do this.

Some top tether points are unhelpfully placed in the middle of the boot of the car, which can stop you from putting luggage in your boot. 

Car seat fitting lists

Some car seat manufacturers publish a list of cars that their car seats should be suitable for. 

Child car seat fitting lists

You can search the Britax fit finder by vehicle or the car seat you are interested in

They can take the form of:

  • online fit finders that allow you to search by your car model
  • vehicle application lists - a list of suitable cars.

But we've found that even the same model of car can vary because manufacturers use different factories and components. 

So although these online guides can be useful, they're just a guide - you should still test a car seat in your car before you buy.

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