Diono Radian VS Graco SlimFit – Comprehensive Comparison

Slim Car Seats – Graco VS Diono, the Biggest Rivals, Any Difference?

In the world of vehicles and child car seats, one of the hassles for parents is getting the right car seat that fits well, especially when you need up to three child seats in the back row.

Be it a compact, mid-size or big vehicle, fitting three car seats can be challenging if you are not deliberate about your choice of safety restraint.

The best convertible seats that fit three across in a vehicle are compact or slim child seats, hence this Graco Slimfit vs Diono Radian comparison, the two most popular and slimmest convertible car seat brands at 16.7″ and 17″, respectively.

The biggest contenders in the market for compact convertible car seats remain the Diono Radian 3RXT and Graco SlimFit3 LX. While both seats may be comparatively slim, they may only fit well in some vehicles because of their unique features.

You will learn in detail the difference and similarities in both car seats, including their:

  • Safety ratings and features
  • Installation features
  • Ease-of-use features
  • Recommended weight and height limit, and seat modes
  • Seat dimensions,
  • Height clearance and how they may affect the front passenger when rear-facing
  • Product weights and your convenience when switching between vehicles, and
  • How they fit in your vehicle in their different seat modes,

While choosing between the Diono Radian vs Graco SlimFit car seats would have been difficult for you, this detailed comparison takes off the burden, and you can make a clearer and easy buying decision.

One significant difference you should note between the Graco SlimFit 3 LX vs Diono Radian 3RXT is the pricing. The latter is significantly more expensive than the former. Other differences are in the dimensions and features.

Read on to learn more about both seats as I help you make a decision.

Overview of Both Car Seats

radian 3rxt vs slimfit3 lx 3-in-1

Diono Radian R & Q Series – Acclaimed 3-across Seats – is that true?

The Radian R & Q car seat series belong to the Diono Radian 3-across category of all-in-one convertibles and include the very popular Radian 3RXT.

The Radian series is the first three across car seats in the child safety seat industry.

The R & Q series consists of seven car seats which can be confusing because of their variants and somewhat similar features. They include:

R series:

  1. 3R
  2. 3RX
  3. 3RXT
  4. 3RXT Safe+

Q series:

  1. 3QX
  2. 3QXT
  3. 3QXT+

A detailed review of the R & Q series, including comparisons among different twos or more seats, can be found here.

As an overview, the significant differences across the safety seat series are:

  • Product weight: the least weight is 28.1 lbs., while the heaviest weighs 34.2 lbs.
  • Ease-of-use features
  • And extra safety features as the model advances

On the one hand, the common similarity in the R & Q series, including the 3RXT, is the dimension. They all have the same dimension – 16″ D x 28.5″ H x 17″ W. They measure 17″ in width, which makes them a good fit for three across in most vehicles.

On the other hand, the Radian seat height (28.5″ H) may not make a good fit in your vehicle when rear-facing.

You need to measure the back seat, door-to-door, to know the dimension and then compare with the total width of 3-radian seats, which is 51″.

This comparison article focuses on the Diono Radian 3RXT variant.

There is also the Radian® 3RXT Safe+® which is an upgrade of the 3RXT by about 18 features – including more extended usage, safety, and ease-of-use features.

diono 3rxt vs 3rxt safe

On the tables you’ll find later, an extra column is added for the 3QXT variant and the Radian® 3RXT Safe+® upgrade.

Graco SlimFit3 LX: The Budget-friendly Option with Better RF Fitting – Do Reconsider

slimfit3 LX 3 in 1 car seat

Graco SlimFit, being a newer model to the market than the Diono Radian and more budget-friendly, took cognizance of the limitation of the existing slim car seats to make a slight yet significant improvement, which was in;

  • Width dimension,
  • Height clearance and
  • Product weight

The Graco SlimFit3 LX 3-in-1 car seat should not be confused with the basic variant, which is the SlimFit 3-in-1, which weighs slightly more and is wider – 19.9″.

Graco consolidates all its premium features, such as safety, installation, ease-of-use features, and comfy fabric, into a single car seat at a friendly price.

This gives it an edge when your need is to be met by your budget, especially since you will likely buy three car seats at a go.

This comparison article also focuses on the Graco SlimFit3 LX variant.

Comparative Analysis of Both Seats – Taking Away Bias out of the Equation

While deciding which of the seats you would choose, you may be biased towards a brand or sentimental about some features over another from a different model/variant or brand.

This is more common with older parents who already love a brand.

On a lighter note, you can be open-minded and flexible to changes, as that brand you don’t really like may have as good features as a more expensive rival. Or, the more expensive model may be ‘overpriced,’ with extra features you may not need.

As you read on in this SlimFit 3 LX vs Diono Radian 3RXT comparison, you will learn and understand both car seats better with an objective mind.

radian 3rxt vs slimfit3 lx 3 in 1

Specification Comparison: Graco SlimFit3 LX VS Diono Radian 3RXT – Similarities & Differences

SpecificationsSlimFit3 LX 3-in-1Radian 3RXT all-in-13RXT Safe+® (upgrade)
Product dimensions 20.7″D x 24.5″H x 16.7″W 16″D X 28.5″H X 17″W 16″D X 28.5″H X 17″W
Product weight 19.2 lbs. 28.1 lbs. 30.6 lbs.
Seat modes 3-in-1
  • rear-facing
  • forward-facing
  • booster seat mode
  • rear-facing for newborn
  • extended rear-facing up to 50 lbs.
  • forward-facing up to 65 lbs.
  • booster seat mode 40-120 lbs.
  • rear-facing for newborn
  • extended rear-facing up to 4 lbs. – 50 lbs.
  • forward-facing up to 65 lbs.
  • booster seat mode 40-120 lbs.
Recommended weight range 5 – 100 lbs. 5 – 120 lbs. 4 – 120 lbs.
Recommended height limit 57″ 57″ 57″
Rear-facing weight limit

min. 5 lbs.; max. 40 lbs.

min. 5 lbs.; max. 50 lbs. (extended usage in RF) min. 4 lbs.; max. 50 lbs. (extended usage in RF)
Rear-facing height limitmin. 19″; max. 40″min. 19″; max. 44″ (extended usage in RF)min. 19″; max. 44″ (extended usage in RF)
Forward-facing weight limit min. 22 lbs.; max. 65 lb.min. 22 lbs.; max. 65 lb.min. 22 lbs.; max. 65 lb.
Forward-facing height limit min. 29″; max. 49″min. 29″; max. 49″min. 29″; max. 49″
Highback booster seat weight limitmin. 40 lbs.; max. 100 lbs.min. 40 lbs.; max. 120 lbs. min. 40 lbs.; max. 120 lbs.
Booster seat height limitmin. 43 in.; max. 57 in.min. 43 in.; max. 57 in.min. 43 in.; max. 57 in
ParentingWithHumility Rating8.0/10
PriceCheck on AmazonCheck on AmazonCheck on Amazon
PriceCheck on WalmartCheck on WalmartCheck on Walmart

NHTSA Ease-of-Use Rating

The National Highway Transport and Safety Agency (NHTSA) provides a simple evaluation of car seats based on how easy it is to use different features in different modes. There is an overall ease-of-use rating for each seat to help you make a quick and informed decision.

This rating is based on four categories:

  1. Evaluation of Instructions
  2. Vehicle Installation Features
  3. Evaluation of Labels
  4. Securing the child


  • 5 Stars = Excellent features
  • 4 Stars = Above-average features
  • 3 Stars = Average features
  • 2 Stars = Below-average features
  • 1 Star = Poor features
  • N/A = Does not contain any features that require a rating
Rear-facing – overall rating⭐⭐⭐⭐⭐
Forward-facing – overall rating⭐⭐⭐⭐⭐
Booster – overall rating⭐⭐⭐⭐⭐⭐

General Features Comparison – SlimFit3 LX VS 3RXT

Safety Features

Safety featuresSlimFit3 LX3RXT3RXT Safe+®
Side Impact Protection ✔ Advanced Safe+ side impact protection (6 layers)
5-point Harness System
Exceeds federal safety standards

Crash tested

Extra tests (frontal, side, rear-impacts, and rollover crash tests) Graco ProtectPlus Engineered

✔Diono Safe+ Engineering impact protection (combination of the most rigorous crash tests)

IIHS rating for Booster seat mode✔✔ Best Bet✔✔ Best Bet✔✔ Best Bet
Specific brand safety feature✔ Graco ProtectPlus Engineered✔ Diono Engineering

✔Diono Safe+ engineering,Safe+ anti-rebound bar, andAdvanced Safe+ side impact protectionSafe+ 6-Layers

Installation Features

Installation featuresSlimFit3 LX3RXT3RXT Safe+®
LATCH/LUAS/ISOFIX system ✔ + InRight™ LATCH attachment – easy installation with LATCH ✔ +SuperLATCH system connectors – easy installation with LATCH ✔ +SuperLATCH system connectors – easy installation with LATCH
Safety seat belt integrated belt lock-off system (easier installation with belt) standard seat beltstandard seat belt

Ease-of-Use Features

Ease-of-Use featuresSlimFit3 LX3RXT & Safe+
Fits 3 Across Back Seat

Harness storage

Harness holders
(to hold harness back while getting your child out of the seat)
Harness adjustment✔ Simply Safe Adjust™ Harness System (10 positions) One-hand easy-to-adjust headrest (12 positions)
No-rethreading of harness

Machine washable

Car seat cover✔ Easy to remove
✔✔ the SlimFit3 LX features the Rapid Remove cover (easier)
✔ Easy to remove
Headrest adjustment10 positions 12 positions
Recline positions4 positionsReclines 30-36″
Recline Level IndicatorBubble
Rear-facing recline position
  • Position 1 – best for newbornPosition 2
Reclines 30-36″
Forward-facing recline position
  • Position 3
  • Position 4
Booster seat recline position
  • Position 4
Removable cups2 (rotatable)1 (you can buy an additional cup)

Comfortability of a Child

ComfortabilitySlimFit3 LX3RXT & Safe+
Soft plush fabric Polyester blend
Removable newborn inserts (travel high wedge) 2
  • 3RXT: 1 (2-in-1 head support)Safe+: 2 (2-in-1 head & body support)
Breathable Mesh AirFlowAvailable (SlimFit3 LX 3-in-1 ONLY)

Longevity, Suitability and Compatibility

Longevity & Suitability featuresSlimFit3 LX3RXT & Safe+
Expiration10 years (from Date of Manufacture) 10 years (from Date of Manufacture)
FAA Approved (RF & FF only)
Suitable country by law USA USA & more
Vehicle compatibilityCompatible with small, compact, mid-size, full-size, vans and SUVs vehicles in all seat modes in any combination Compatible with compact, mid-size, full-size, vans and SUVs vehicles in similar seat mode combination (more ideal in ff & booster modes)

Miscellaneous features

ComfortabilitySlimFit3 LX3RXT & Safe+
Available colors


Country of OriginChinaChina
Body frameworkSteel-reinforced frame Steel-reinforced frame

Analysis of Both Seats in Detail – Which is the Winner? – Helping You Make a Decision

radian 3rxt vs slimfit3 lx 3 in 1

Now we have gone through different tables highlighting the similarities and differences in both safety seats, including the upgraded 3RXT Safe+.

You will observe that beyond the slim designs of the seats, they differ in other specifications and features, though somewhat close.

At this point, making a decision becomes paramount. I’ll cover this section to highlight every aspect of both seats and make a detailed analysis that can help your final decision-making process.

Which seat wins?

The significant difference in both seats, which isn’t so obvious from the tables, is the dimension (height, H). Other significant areas are product weight, seat mode weight, ease of use features, and pricing.

Specification Comparison

Product Dimensions

Despite both seats being slim, their width is slightly different. The SlimFit3 LX measures 16.7” wide, while the Diono Radian 3RXT is 17″.

This is important if you already have other seats in your vehicle and considering a third one.

Diono themselves recommend using their car seats as a combination in threes. That means there may be a challenge fitting a Radian if your other seats are already wide.

However, the SlimFit3 offers you a better chance of fitting as the third seat in a row.

On the other hand, when it comes to seat height, the Radian 3 RXT measures 28.5″ in height, while the SlimFit3 measures 24.5″.

This is a significant difference as it affects your front passenger seat when rear-facing.

This is one common complaint among parents using the Diono Radian in their vehicles, especially compact and mid-size vehicles.

The SlimFit saves you more space when RF, irrespective of seat position.

On this, the SlimFit3 LX 3-in-1 wins by a wide margin.

Product Weight

While convertible car seats are relatively bulky compared to infant seats, some come lightweight.

Consider how bulky your convertible seat is if you often switch between vehicles.

At a whopping difference of about 9 lbs. (slim fit < 3RXT), or 11.4 lbs. (slim fit < 3RXT Safe+), you should rethink which car seat you’d go for.

On the other hand, the Radian car seat can be folded for storage when not in use or for convenient travel. The bulky weight doesn’t still give it an edge.

In this case, SlimFit3 LX wins once again.

Seat Modes, Weight, and Height Limits

Diono Radian claim their child seats to be 4-in-1 (all-in-1 as they call it), but it is still the regular 3-in-1 car seat as the Graco SlimFit that is used in rear-, forward-facing and as a highback booster seat.

A 4-in-1 seat is a convertible car seat that has an additional backless booster seat mode.

Nonetheless, Diono safety restraints offer extended usage in rear-facing up to 50 lbs. just like the Graco Extend2Fit. The upgraded model (Safe+) offers even more friendly usage for preemies at 4 lbs. unlike the 3RXT and SlimFit at 5 lbs.

The Radians also have a max weight limit of 120 lbs., while the SlimFit sits at 100 lbs.

The 3RXTs also have an extended height limit of 44″ in RF as against Slim Fit at 40″.

This gives the Diono Radian RXT its first win.

diono 3rxt vs 3rxt safe

Features Comparison

Safety Features

This is one of the most critical features parents look into when buying a car seat.

That is understandable, as we want absolute safety for our little ones.

The federal government wants this for us too, and therefore subject car seat manufacturers to very stringent safety standards to ensure every child seat on the market is certified safe.

Beyond this, manufacturers go overboard to add more safety features and perform even more rigorous crash tests. Different brands patent their safety techniques as they use different standard procedures.

Safe to say, all car seats are SAFE, as always emphasized here on ParentingWithHumility (disclaimer: personal opinion).

None of the seats is given a win here.

Crash Testing

As mentioned earlier, car set manufacturers add more safety features to their products and conduct rigorous crash tests.

Graco brand calls theirs “Graco® ProtectPlus Engineered™” while Diono calls theirs “Diono Engineering” in the 3RXT and “Diono Safe+ Engineering” in the upgraded model, 3RXT Safe+.

The Graco ProtectPlus Engineering combines the most rigorous crash tests in frontal-, side-, rear-impacts, and rollover crashes. Their rollover tests (Graco RollSafe™) follow the European rollover standard procedure.

The Diono Safe+ Engineering also involves “a combination of the most rigorous crash tests.” However, this particular safety standard is available in the upgraded model and not the basic 3RXT, which raises the question of why.

The safety features of the 3 RXT are not elaborated by Diono, unlike Graco, which gives the SlimFit 3 LX an upper hand.

IIHS Rating

IIHS rates car seats’ ease of use in booster mode.

Diono Radian RXT and Graco SlimFit are rated “BEST Bet,” which means they are easy to use in booster seat mode.

NHTSA Ease-of-Use Rating

NHSTA, on the other hand, rates car seats on a broad scale of how easy it is to use different features through each seat mode.

The SlimFit ranks higher through all seat modes than the 3RXT.

While Graco SlimFit is rated 4 stars, 3 stars, and 4 stars, respectively, in the overall rear-, forward-facing, and booster seat modes, the Diono 3RXT is rated 2 stars all through.

Despite these ratings, practical feedbacks from parents say otherwise. Both car seats receive high praise from parents in practical usage, installation, and safety in all seat modes.

However, the SlimFit 3 LX still takes the win here again.

Installation Features

For a car seat to protect a child optimally in a car crash, the safety seat must be securely installed in the vehicle. A seat should only move up to 1cm when moved front-to-back or side-to-side.

To ensure proper installation, the installation features come in handy.

With its seat belt installation feature, Graco SlimFit has the edge over its Diono counterpart.

While both seats offer easy LATCH installation features, the InRight™ LATCH attachment and SuperLATCH connectors, the Radian 3RXT offers just the standard seat belt installation feature.

On the other hand, the SlimFit3 LX features the integrated belt lock-off system, which is an easier method than the standard.

Graco SlimFit wins here.

Side Impact Protection, 5-point Harness System

These are critical safety features in a car seat.

Both seats feature the 5-point harness system and side-impact protection.

However, the upgraded Diono model offers 6-layers in its side-impact protection.

As you may already know, the Radian is more expensive than the Graco. The upgraded model is even costlier.

The outcome here is a tie.

Ease-of-Use Features

Going over the tables again, the SlimFit3 LX has more ease-of-use features than the 3RXT, including the upgraded variant.

The Graco SlimFit3 LX, like other of their models, features a harness storage compartment to store the harness when not in use and harness holders to hold back the harness when you are carrying your child out of the seat. This is so convenient, especially for a first-time parent/car seat owner.

Another plus the SlimFit offers are the reclining positions that give it a better fit in a vehicle and offer more comfort for a child. Though the Radian reclines up to 30-36″ in rear-facing, you need to buy a separate angle adjuster to enjoy this feature. On the other hand, Graco reclines differently and easily in all seat modes.

The machine washable and easy-to-remove seat covers are shared features in both seats. The Graco’s remove more easily under 60 seconds (Rapid Remove Cover).

The Diono has two extra headrest positions over Graco’s 10. However, Graco comes with two cups that fit in 3 across configurations, whereas Diono comes with only one, and you need to buy the other.

The Graco SlimFit 3 LX 3-in-1 wins by a slide.

Comfortability for a Child

Both seats are comfortable for a child, which is a good thing.

A little difference makes a real difference in the end.

The Graco SlimFit comes in soft plush fabric, which is more comfortable for a child than the polyester blend in the 3RXT.

The SlimFit also comes with two removable newborn inserts (head and body support), called high travel wedge in the Radian. However, the Radian 3RXT comes with only head support. The 3RXT Safe+ comes with both head and body support but at a premium.

The icing on the cake for the SlimFit3 LX is the Breathable Mesh AirFlow which allows for better ventilation for a child. This is an advantage during the summer when you need to keep your child cool in car seat.

Here again, the SlimFit3 LX wins.


Both seats come as a tie here.

The 3RXT and Graco SlimFit have expiration dates of 10 years from their date of manufacture.

They both have reinforced steel which gives them this long duration for usage.

Either of the seats will be the only seat you may need for your child through their growing years.

FAA Approved

The Radian 3RXT and Graco SlimFit are approved for use on an airplane in harness mode.

You are not to use either of the seats on an aircraft in booster seat mode.

Safe air travels.

Final Thought and Recommendations: Making a Choice

Overall, the Graco SlimFit3 LX takes the win in this comparison.

It cannot be overemphasized that despite the higher pricing of the Diono Radian 3RXT or Safe+ upgrade, the SlimFit3 offers more value for money.

Making a final decision at this point will come down to personal preference and budget.

If you are a brand loyalist, you may be more biased toward one model here. Either choice will be a good one as they get the job done perfectly.

If you’re more objective, my recommendation will be the Graco SlimFit3 LX 3-in-1 for the following reasons:

  • It is budget-friendly – you get to save more money for other baby essentials, and your family
  • Lightweight – you don’t have to lift bulky car seats now and then when switching between vehicles or cleaning car seats.
  • Comprehensive safety features – the Graco SlimFit offers all safety features in one pack at reasonable pricing than the Diono, which has an upgraded variant at a higher price
  • And ease of use – this is the critical factor for me. If you are like me that will take convenience at a price, I will go for the SlimFit. And it even comes cheaper.

If you remain undecided, here’s a simple analogy that should help you make a final choice:

  • If you’re budget-conscious and need three car seats at a go, choose the SlimFit.
  • If you need a combination of both brands for practical comparison in the long term, go for two SlimFits and one Radian, which should be installed in the middle rear if rear-facing.
  • If you need a third car seat for your vehicle and want a high-end choice, go for the Diono. If you are on a budget, go for the SlimFit.
  • If you need a preemie-friendly seat or consider rear-facing your child long enough, go for the 3RXT Safe+.
  • If you must go for the Diono and don’t need up to three seats, go for the 3RXT Safe+.

With this detailed comparison of the Diono Radian 3RXT vs Graco SlimFit3 LX, I hope you are able to arrive at a final choice.

You can read more on car seats here, including expiration, installation, reviews, and comparisons.

Cheers to happy parenting.

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