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Baby & child.

Updated: 22 Jun 2021

How to buy a child car seat that fits your car

Not all child car seats fit all cars. Find out why, and what else you need to think about before buying the best car seat for your baby and you.
Hannah Fox
Infant carrier, group 1 and High backed booster

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 not all car seats fit in all cars.

Here we let you know what to look out for before you buy a baby or child car seat to fit your car. If you've already bought your baby or child car seat, head straight to our guide on how to fit a car seat: 10 essential checks.

Discover which car seats are Best Buys and which we've labelled Don't Buys by visiting our car seat reviews

How can I find a child car seat that fits?

The best way to do this is to get a qualified 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.

How to buy the best child car seat – get more practical tips about the buying process.

woman fitting car seat in car

Why 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

If you're going to have more than one child in your car, you'll need to make sure that multiple seats will safely fit across the rear seat of your car. Most cars can fit two child car seats but, if you've got three children and a small car, you could have issues.

Height of front-seat passengers

Tall passengers in the front, and a car seat in the back generally don't make a good combination. If you've got a car seat with a base that uses a support leg, or an extended rear-facing model, then check that you can still use the front passenger seat, especially if you have a partner who's particularly lofty.

girl in driving seat

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 inside the car and features of the car can all prevent a seat from fitting properly.


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

Best child car seats – we crash test car seats to find the best and worst.

airbag warning label

Space in the car

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

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

Lap belts

Some old cars still have a lapbelt seat belt for the middle rear seat, rather than a standard three-point seat belt. Generally, for safety reasons, a lapbelt seatbelt can't be used to attach a car seat. Using a lap-only belt could cause the seat to flip over in a crash.


Car headrests can cause problems with child car seats. The car's headrest shouldn't interfere with the child car seat, so when a child seat is fitted, it should sit flush against the back of the seat. The head rest shouldn't touch the seat and it shouldn't stop the car seat from touching the car seat fabric.

Either pull the car's headrest well out the way, or remove it if you can. If the headrest gets in the way and cannot be removed, you may not be able to use a child car seat in that seat.

Don't wedge your child's car seat under the car's head rest - it will stop it working in a crash.

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.

child sleeping in car seat

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.

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 fastened.

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 that the car seat is being held by the fabric part of the seatbelt - the webbing - rather than by the buckle. In the event of a crash, the seatbelt fabric will stretch to help absorb the impact.

buckle crunch

Seatbelt length

Some seatbelts aren't 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

Car seats are shaped to pull passengers into them, so many rear seats 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.

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

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

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.

Isofix connectors close up

Isofix car seats - what you need to know

Isofix child car seats are usually used with a support leg or top tether to prevent the seat tipping over on the Isofix mounts in a crash, which would place strain on your child's back and neck. 

Underfloor storage compartments

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

The lid of the storage compartment isn't strong enough to withstand 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.

rear facing car seat top tether

Top tether anchor 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 anchor point that's been designed to withstand the force of a child car seat pulling away from it in a crash.

Headrests are not designed to do this.

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

Car seat fitting lists

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

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 try a car seat in your car before you buy.

Child car seat safety featuresget to grips with the safety features of each type of seat