Are you trying to fit three kids across the back seat of your vehicle? You’ve probably found that car seat selection matters a whole lot in this situation, where space is limited. We’ve created this list of the narrowest boosters currently on the market in the US, to help you find one that might work for your vehicle.

UPDATE: Unfortunately, some of the narrowest boosters shown here have recently been discontinued. You may still be able to locate them locally. Why are the most useful boosters being discontinued? We don’t know, and we share your frustration. 

Note: Using a booster in a three across situation adds an extra problem–getting your (or your child’s) hand in between the car seats to buckle the booster child’s seat belt. At the bottom of the page you can find a video of how to avoid dealing with buckling the seat belt when space is tight–by teaching your child how to climb in and out of an already-buckled seat belt.

High Back Boosters

We know these high back boosters aren’t budget friendly….but if you have a narrow spot where you need to fit a high back booster, you (sadly) don’t have many options. Having done hundreds of 3-across scenarios, we can say the Maxi Cosi Rodifix is the most likely high back booster to fit – and if the Rodifix doesn’t fit, there is literally NO other high back booster that will. 

DISCONTINUED! Please note that the replacement booster, the Rodisport, is not the same as the Rodifix.

The most versatile high back option: To say we love the Rodifix would be an understatement. It’s the most versatile booster we’ve found (and we’ve tried them all).

Extremely narrow but still super comfy!!: Rodifix has the narrowest footprint and flexible sides, making it more likely to fit in narrow seating positions where other boosters won’t. At the same time it still accommodates wider kids fabulously due to its flexible sides and an absence of arm rests. If space is at a premium in your vehicle, then this is the seat to consider. If the Rodifix doesn’t fit, there is no other high back booster in the US will. 

Thoughtful design to avoid misuse: This booster’s design has eliminated the most common (and most serious) misuse of all boosters: when someone accidentally puts the lap belt over one or both of the arm rests. Doing this puts the lap belt across the child’s belly, which is a dangerous misplacement that can cause severe injury or death in a crash. Because this booster doesn’t have arm rests, you can’t make this mistake when buckling up! The lack of arm rests also makes it easier for a child to see the buckle and to get their hand in to buckle and unbuckle themselves independently–something both kids and parents love.

Excellent head rest: The head rest is so well designed on the Rodifix that we’d love to use it ourselves! It captures the head perfectly so your kid’s head won’t be bobbing around during sleep. Keeping the head well positioned during sleep is an important part of keeping the whole body properly positioned in the seat belt – because if the head falls, sometimes the torso starts to fall forward or slump sideways, both of which are dangerous as the seat belt then won’t be on the proper part of the child’s body.

High back only. Does not turn into a backless booster.

Rigid back works with low vehicle headrests. The back of this booster is rigid enough to support the child’s head and does not need the vehicle seat back to come up to the child’s ears for whiplash protection. It also handles vehicle head rests that protrude better than most other boosters.

LATCH: Rodifix can be secured to the vehicle using rigid lower anchor connectors (rigid LATCH). Note that it is not required to secure this or any other booster to lower anchors.

Longevity: Most kids will fit in the Rodifix until somewhere between 8-10 years old, at which point they will likely move into a backless booster or pass the 5-Step Test. 

Narrow but with super high weight and height limits: For a booster that accommodates the tallest child of any high back booster in the US market, the Shuttle Plus 120 is surprisingly slim on the outside compared to most others (it’s still definitely wider than the Rodifix). The Shuttle Plus 120 has the highest capacity for both height and weight of any high back booster in the US. If you have a child with a very tall torso, they’ll fit in this booster longer than any other.

Adjustable width: You can adjust the width of the side panels, which helps make the seat more narrow when there isn’t much room in the vehicle.

Well designed armrests: While there are arm rests on this booster, they are spaced far enough apart that many wider kids should be comfortable.

Rigid back works with low vehicle head rests: The back of this booster is rigid enough to support the child’s head and does not need the vehicle seat back to come up to the child’s ears for whiplash protection.

2 in 1: The back can be removed to turn this into a backless booster

LATCH: This booster can be secured to the vehicle using rigid lower anchor connectors (rigid LATCH). Please note that it’s never required to secure this or any other booster to the lower anchors in a vehicle.

Longevity: Most kids will fit in this booster until 10-12 years old before becoming too tall for it. 

Check Fit in High Back Mode: The shoulder belt guides on this booster are fairly wide. Double-check that the seat belt fits your child properly when they are using this booster in high back mode (you should be doing this for all boosters no matter what, but it is especially important to note here, according to IIHS booster fit testing)

Less expensive, narrow option: Of the less expensive high back boosters, the Turbo TakeAlong is most likely to fit in a narrow spot 

Longevity is limited: Your child will outgrow the seat’s high back booster mode sooner than the other boosters featured on this page because the Turbo TakeAlong’s top shoulder belt setting is quite low (and all kids are typically too tall long before they’re too heavy for a high back booster). 

Difficult to buckle in tight spaces: It will often be very difficult to get your hand in to buckle the child in this booster when used in a narrow spot. You may want to use the trick in the video at the bottom of this page.

2 in 1 but wide in backless mode: The back can be removed to turn the Turbo TakeAlong into a backless booster, but it’s on the wider side. if you don’t have much room in your vehicle and you need a backless booster, one of the narrow backless boosters highlighted below would be a much better option than this one in backless mode.

We know this is not a dedicated booster!

But it’s so narrow, and so many of our previous choices have been discontinued, that we decided to put it on the list, since it has a booster mode that can be used for a reasonable period of time. It’s not going to last forever and your child will almost certainly need another booster after they outgrow it, but it may allow your 3-across set up to work for a while until you change your vehicle or another child moves into a different seat, freeing up space for the child using this seat to move into a longer lasting one.

For example, if you have a booster ready child, a toddler, and a new baby on the way, this seat may get you a 3 across set up for another year until the baby moves out of their infant seat (and perhaps into this seat), at which point the child using this seat would move into something larger.

Super narrow footprint and width: Probably the narrowest seat out there right now! Cupholders are removable to make the seat even more narrow.

LATCH installation in booster mode: Permitted but not required.

Height Limit: 57 inches in booster mode

Weigh Limit: 100 lbs

Top shoulder belt guide height: 18.5 inches

Note: When purchasing, make sure you are getting this seat, the Slimfit3LX, and not the similarly named Slimfit 3-in-1, or SlimfitLX 3-in-1, which are completely different seats that aren’t very slim despite their misleading names. Be very careful, the three seats are often listed together on the same Amazon product page! The Slimfit3LX has a gray lever on its headrest and a small black base that is more narrow than the actual seat, with a grey lever to adjust the seat’s recline angle. The Slimfit 3-in-1 has a red lever on its headrest and a wide base with a red lever to adjust the recline angle. The SlimfitLX 3-in-1 has a grey lever on its headrest (so be really careful here) but a wider base than the Slimfit3LX you actually intend to purchase.

Backless Boosters

Remember: In order to use a backless booster, you need to make sure the vehicle seat back comes up to at least the top of the child’s ears so it can provide adequate head support. If the vehicle seat back does NOT come up to at least the top of the child’s ears, then your child needs to use a high back booster in that seating position.

Narrowest option out of all available boosters: The RightGuide has the narrowest footprint out of all high back or backless boosters currently on the market in the US, making it a great option for narrow centers or for squeezing next to another car seat where other boosters wouldn’t fit. 

Excellent design and fit to enhance safety: We like this booster for more than just it’s small size. We can say with no exaggeration that the RightGuide is the best thing we’ve ever seen in the category of backless boosters.The Rightguide fits both skinny and wider kids very well due to the lateral flexibility in the red belt guides. It has a slight upwards slant at the knees which enhances comfort and therefore safety, as it helps prevent kids from wanting to slouch (slouching puts the lap belt on the belly, which is dangerous!).

Extremely travel-friendly: The RightGuide is a fabulous choice for travel, playdates, and carpool. Weighing just 1.8 lbs and the size of a laptop, it easily slides into a child’s backpack and many purses, diaper bags, tote bags, etc. The red belt guides fold flush with the underside of the booster to make it super compact for carrying around when you aren’t in a car. We’ve traveled extensively both in the US and internationally with this booster, in a wide variety of vehicles, and have been very pleased with its convenience and performance.

IIHS: This booster has not yet been evaluated by IIHS… but in our informal testing of it with a variety of kids we have found that it offers a great belt fit for small and large kids in a variety of vehicles.


Vertical lap belt guides save space and add comfort: Turbo Go features completely vertical and very high lap belt guides, which make the seat more likely to fit in between others. These guides also better accommodate kids with bigger thighs. Because the guides sit higher than the child’s thighs and are not tapered, they don’t push into the child’s thighs the same way other booster belt guides do. 

Comfort for bigger kids: Generous width and longer-than-average seat depth accommodate kids with longer legs. Note: the longer seat depth poses a potential problem for younger children as their knees may not bend naturally over the edge without slouching. 

Travel friendly: This booster weighs 4 pounds and folds, so it fits nicely in a large backpack.

Lifts kids up: Turbo Go boosts the child up a fair amount (more so than the RightGuide) which is great for shorter kids. Note that this added height can be an issue for a taller kid if their head starts getting too close to the roof of the car or their head isn’t supported by the vehicle seat back or vehicle head restraint.

Harmony Youth IIHS best bet

Narrow and lightweight: The Harmony Youth and Cosco Rise are both very lightweight and inexpensive narrow backless boosters. Due to differences in their contouring, one might fit better than the other in a specific narrow spot in your vehicle. 

The Rise has a shallower seat depth than the Youth – so the Rise is better for shorter kids and won’t fit taller kids as well.

Cosco has released a new version of the Rise called the Rise LX, which differs only in its more plush and more plentiful padding. It’s sold at Walmart.

Both boosters get a Best Bet from IIHS in their booster evaluations. 

Can't get your hand in to buckle the booster?

Try having the child climb in/out without unbuckling the seat belt.

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FTC Disclosure: Affiliate links are included in this page. No monetary compensation was provided, however, some of the reviewed products were supplied by the manufacturer or distributor to help facilitate the review. All opinions are those of The Car Seat Lady LLC.